diff --git a/includes/class-newspack-newsletters-ads.php b/includes/class-newspack-newsletters-ads.php
index 2ace23217..53b435154 100644
--- a/includes/class-newspack-newsletters-ads.php
+++ b/includes/class-newspack-newsletters-ads.php
@@ -75,21 +75,11 @@ public static function rest_api_init() {
 			[
 				'callback'            => [ __CLASS__, 'get_ads_config' ],
 				'methods'             => 'GET',
-				'permission_callback' => [ __CLASS__, 'permission_callback' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 			]
 		);
 	}
 
-	/**
-	 * Check capabilities for using the API for authoring tasks.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return bool|WP_Error
-	 */
-	public static function permission_callback( $request ) {
-		return current_user_can( 'edit_posts' );
-	}
-
 	/**
 	 * Register custom fields.
 	 */
diff --git a/includes/class-newspack-newsletters-editor.php b/includes/class-newspack-newsletters-editor.php
index 711edc7d7..526966095 100644
--- a/includes/class-newspack-newsletters-editor.php
+++ b/includes/class-newspack-newsletters-editor.php
@@ -338,6 +338,7 @@ public static function enqueue_block_editor_assets() {
 				'byline_connector_label' => __( 'and ', 'newspack-newsletters' ),
 			],
 			'supported_social_icon_services' => Newspack_Newsletters_Renderer::get_supported_social_icons_services(),
+			'supported_esps'                 => Newspack_Newsletters::get_supported_providers(),
 		];
 
 		if ( self::is_editing_email() ) {
@@ -381,6 +382,7 @@ public static function enqueue_block_editor_assets() {
 					'is_service_provider_configured' => Newspack_Newsletters::is_service_provider_configured(),
 					'service_provider'               => Newspack_Newsletters::service_provider(),
 					'user_test_emails'               => self::get_current_user_test_emails(),
+					'labels'                         => $provider ? $provider::get_labels() : [],
 				]
 			);
 			wp_register_style(
diff --git a/includes/class-newspack-newsletters-subscription.php b/includes/class-newspack-newsletters-subscription.php
index 2867e6271..865d5f4f6 100644
--- a/includes/class-newspack-newsletters-subscription.php
+++ b/includes/class-newspack-newsletters-subscription.php
@@ -73,7 +73,7 @@ public static function register_api_endpoints() {
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ __CLASS__, 'api_get_lists' ],
-				'permission_callback' => [ 'Newspack_Newsletters', 'api_permission_callback' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_administration_permissions_check' ],
 			]
 		);
 		register_rest_route(
@@ -82,7 +82,7 @@ public static function register_api_endpoints() {
 			[
 				'methods'             => \WP_REST_Server::EDITABLE,
 				'callback'            => [ __CLASS__, 'api_update_lists' ],
-				'permission_callback' => [ 'Newspack_Newsletters', 'api_permission_callback' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_administration_permissions_check' ],
 				'args'                => [
 					'lists' => [
 						'type'     => 'array',
diff --git a/includes/class-newspack-newsletters.php b/includes/class-newspack-newsletters.php
index 78d3f83c2..6e333f498 100644
--- a/includes/class-newspack-newsletters.php
+++ b/includes/class-newspack-newsletters.php
@@ -267,6 +267,7 @@ public static function register_meta() {
 				'type'           => 'string',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
+				'default'        => '',
 			]
 		);
 		\register_meta(
@@ -285,6 +286,70 @@ public static function register_meta() {
 				'default'        => -1,
 			]
 		);
+		\register_meta(
+			'post',
+			'send_list_id',
+			[
+				'object_subtype' => self::NEWSPACK_NEWSLETTERS_CPT,
+				'show_in_rest'   => [
+					'schema' => [
+						'context' => [ 'edit' ],
+					],
+				],
+				'type'           => 'string',
+				'single'         => true,
+				'auth_callback'  => '__return_true',
+				'default'        => '',
+			]
+		);
+		\register_meta(
+			'post',
+			'send_sublist_id',
+			[
+				'object_subtype' => self::NEWSPACK_NEWSLETTERS_CPT,
+				'show_in_rest'   => [
+					'schema' => [
+						'context' => [ 'edit' ],
+					],
+				],
+				'type'           => 'string',
+				'single'         => true,
+				'auth_callback'  => '__return_true',
+				'default'        => '',
+			]
+		);
+		\register_meta(
+			'post',
+			'senderName',
+			[
+				'object_subtype' => self::NEWSPACK_NEWSLETTERS_CPT,
+				'show_in_rest'   => [
+					'schema' => [
+						'context' => [ 'edit' ],
+					],
+				],
+				'type'           => 'string',
+				'single'         => true,
+				'auth_callback'  => '__return_true',
+				'default'        => '',
+			]
+		);
+		\register_meta(
+			'post',
+			'senderEmail',
+			[
+				'object_subtype' => self::NEWSPACK_NEWSLETTERS_CPT,
+				'show_in_rest'   => [
+					'schema' => [
+						'context' => [ 'edit' ],
+					],
+				],
+				'type'           => 'string',
+				'single'         => true,
+				'auth_callback'  => '__return_true',
+				'default'        => '',
+			]
+		);
 		\register_meta(
 			'post',
 			'newsletter_sent',
@@ -314,6 +379,7 @@ public static function register_meta() {
 				'type'           => 'string',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
+				'default'        => '',
 			]
 		);
 		\register_meta(
@@ -329,6 +395,7 @@ public static function register_meta() {
 				'type'           => 'string',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
+				'default'        => '',
 			]
 		);
 		\register_meta(
@@ -344,6 +411,7 @@ public static function register_meta() {
 				'type'           => 'string',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
+				'default'        => '',
 			]
 		);
 		\register_meta(
@@ -359,6 +427,7 @@ public static function register_meta() {
 				'type'           => 'string',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
+				'default'        => '',
 			]
 		);
 		\register_meta(
@@ -374,6 +443,7 @@ public static function register_meta() {
 				'type'           => 'boolean',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
+				'default'        => false,
 			]
 		);
 		\register_meta(
@@ -835,15 +905,6 @@ public static function api_set_settings( $request ) {
 		return $wp_error->has_errors() ? $wp_error : self::api_get_settings();
 	}
 
-	/**
-	 * Whether the current user can manage admin settings.
-	 *
-	 * @return bool Whether the current user can manage admin settings.
-	 */
-	public static function api_permission_callback() {
-		return current_user_can( 'manage_options' );
-	}
-
 	/**
 	 * Retrieve settings.
 	 */
diff --git a/includes/class-send-lists.php b/includes/class-send-lists.php
index f93037d46..388772b1e 100644
--- a/includes/class-send-lists.php
+++ b/includes/class-send-lists.php
@@ -8,10 +8,7 @@
 namespace Newspack\Newsletters;
 
 use Newspack_Newsletters;
-use Newspack_Newsletters_Settings;
-use Newspack_Newsletters_Subscription;
 use WP_Error;
-use WP_Post;
 
 defined( 'ABSPATH' ) || exit;
 
@@ -34,7 +31,7 @@ public static function init() {
 			return;
 		}
 
-		add_action( 'rest_api_init', [ __CLASS__, 'register_api_endpoints' ] );
+		\add_action( 'rest_api_init', [ __CLASS__, 'register_api_endpoints' ] );
 	}
 
 	/**
@@ -55,13 +52,13 @@ public static function should_initialize_send_lists() {
 	 * Register the endpoints needed to fetch send lists.
 	 */
 	public static function register_api_endpoints() {
-		register_rest_route(
+		\register_rest_route(
 			Newspack_Newsletters::API_NAMESPACE,
 			'/send-lists',
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ __CLASS__, 'api_get_send_lists' ],
-				'permission_callback' => [ 'Newspack_Newsletters', 'api_permission_callback' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_administration_permissions_check' ],
 				'args'                => [
 					'ids'       => [
 						'type' => [ 'array', 'string' ],
@@ -171,9 +168,15 @@ public static function api_get_send_lists( $request ) {
 		foreach ( $defaults as $key => $value ) {
 			$args[ $key ] = $request[ $key ] ?? $value;
 		}
-
+		$send_lists = $provider->get_send_lists( $args );
 		return \rest_ensure_response(
-			$provider->get_send_lists( $args )
+			\is_wp_error( $send_lists ) ? $send_lists :
+				array_map(
+					function( $send_list ) {
+						return $send_list->to_array();
+					},
+					$send_lists
+				)
 		);
 	}
 }
diff --git a/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign-controller.php b/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign-controller.php
index 3c8172c93..64baaf2d3 100644
--- a/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign-controller.php
+++ b/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign-controller.php
@@ -104,7 +104,7 @@ public function register_routes() {
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ $this, 'api_retrieve' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id' => [
 						'sanitize_callback' => 'absint',
diff --git a/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign.php b/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign.php
index c00dca0a2..c958081ee 100644
--- a/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign.php
+++ b/includes/service-providers/active_campaign/class-newspack-newsletters-active-campaign.php
@@ -7,11 +7,21 @@
 
 defined( 'ABSPATH' ) || exit;
 
+use Newspack\Newsletters\Send_Lists;
+use Newspack\Newsletters\Send_List;
+
 /**
  * ActiveCampaign ESP Class.
  */
 final class Newspack_Newsletters_Active_Campaign extends \Newspack_Newsletters_Service_Provider {
 
+	/**
+	 * Provider name.
+	 *
+	 * @var string
+	 */
+	public $name = 'ActiveCampaign';
+
 	/**
 	 * Cached fields.
 	 *
@@ -26,6 +36,13 @@ final class Newspack_Newsletters_Active_Campaign extends \Newspack_Newsletters_S
 	 */
 	private $lists = null;
 
+	/**
+	 * Cached segments.
+	 *
+	 * @var array
+	 */
+	private $segments = null;
+
 	/**
 	 * Cached contact data.
 	 *
@@ -40,13 +57,6 @@ final class Newspack_Newsletters_Active_Campaign extends \Newspack_Newsletters_S
 	 */
 	public static $support_local_lists = true;
 
-	/**
-	 * Provider name.
-	 *
-	 * @var string
-	 */
-	public $name = 'ActiveCampaign';
-
 	/**
 	 * Class constructor.
 	 */
@@ -495,13 +505,39 @@ public function set_api_credentials( $credentials ) {
 	/**
 	 * Get lists.
 	 *
+	 * @param array $args Query args to pass to the lists_lists endpoint.
+	 *                    For supported args, see: https://www.activecampaign.com/api/example.php?call=list_list.
+	 *
 	 * @return array|WP_Error List of existing lists or error.
 	 */
-	public function get_lists() {
+	public function get_lists( $args = [] ) {
 		if ( null !== $this->lists ) {
+			if ( ! empty( $args['ids'] ) ) {
+				return array_values(
+					array_filter(
+						$this->lists,
+						function ( $list ) use ( $args ) {
+							return Send_Lists::matches_id( $args['ids'], $list['id'] );
+						}
+					)
+				);
+			}
+			if ( ! empty( $args['filters[name]'] ) ) {
+				return array_values(
+					array_filter(
+						$this->lists,
+						function ( $list ) use ( $args ) {
+							return Send_Lists::matches_search( $args['filters[name]'], [ $list['name'] ] );
+						}
+					)
+				);
+			}
 			return $this->lists;
 		}
-		$lists = $this->api_v1_request( 'list_list', 'GET', [ 'query' => [ 'ids' => 'all' ] ] );
+		if ( empty( $args['ids'] ) && empty( $args['filters[name]'] ) ) {
+			$args['ids'] = 'all';
+		}
+		$lists = $this->api_v1_request( 'list_list', 'GET', [ 'query' => $args ] );
 		if ( is_wp_error( $lists ) ) {
 			return $lists;
 		}
@@ -509,43 +545,159 @@ public function get_lists() {
 		unset( $lists['result_code'] );
 		unset( $lists['result_message'] );
 		unset( $lists['result_output'] );
-		$this->lists = array_values( $lists );
-		return $this->lists;
+
+		if ( ! empty( $args['ids'] ) && 'all' === $args['ids'] ) {
+			$this->lists = array_values( $lists );
+		}
+		return array_values( $lists );
+	}
+
+	/**
+	 * Get all applicable lists and segments as Send_List objects.
+	 *
+	 * @param array $args Array of search args. See Send_Lists::get_default_args() for supported params and default values.
+	 *
+	 * @return Send_List[]|WP_Error Array of Send_List objects on success, or WP_Error object on failure.
+	 */
+	public function get_send_lists( $args = [] ) {
+		$send_lists = [];
+		if ( empty( $args['type'] ) || 'list' === $args['type'] ) {
+			$list_args = [
+				'limit' => ! empty( $args['limit'] ) ? intval( $args['limit'] ) : 100,
+			];
+
+			// Search by IDs.
+			if ( ! empty( $args['ids'] ) ) {
+				$list_args['ids'] = implode( ',', $args['ids'] );
+			}
+
+			// Search by name.
+			if ( ! empty( $args['search'] ) ) {
+				if ( is_array( $args['search'] ) ) {
+					return new WP_Error(
+						'newspack_newsletters_active_campaign_fetch_send_lists',
+						__( 'ActiveCampaign supports searching by a single search term only.', 'newspack-newsletters' )
+					);
+				}
+				$list_args['filters[name]'] = $args['search'];
+			}
+
+			$lists = $this->get_lists( $list_args );
+			if ( is_wp_error( $lists ) ) {
+				return $lists;
+			}
+			foreach ( $lists as $list ) {
+				$send_lists[] = new Send_List(
+					[
+						'provider'    => $this->service,
+						'type'        => 'list',
+						'id'          => $list['id'],
+						'name'        => $list['name'],
+						'entity_type' => 'list',
+						'count'       => $list['subscriber_count'] ?? 0,
+					]
+				);
+			}
+		}
+
+		if ( empty( $args['type'] ) || 'sublist' === $args['type'] ) {
+			$segment_args = [];
+			if ( ! empty( $args['ids'] ) ) {
+				$segment_args['ids'] = $args['ids'];
+			}
+			if ( ! empty( $args['search'] ) ) {
+				$segment_args['search'] = $args['search'];
+			}
+			$segments = $this->get_segments( $segment_args );
+			if ( is_wp_error( $segments ) ) {
+				return $segments;
+			}
+			foreach ( $segments as $segment ) {
+				$segment_name = ! empty( $segment['name'] ) ?
+					$segment['name'] . ' (ID ' . $segment['id'] . ')' :
+					sprintf(
+						// Translators: %s is the segment ID.
+						__( 'Untitled %s', 'newspack-newsletters' ),
+						$segment['id']
+					);
+				$send_lists[] = new Send_List(
+					[
+						'provider'    => $this->service,
+						'type'        => 'sublist',
+						'id'          => $segment['id'],
+						'parent'      => $args['parent'] ?? null,
+						'name'        => $segment_name,
+						'entity_type' => 'segment',
+						'count'       => $segment['subscriber_count'] ?? null,
+					]
+				);
+			}
+		}
+
+		return $send_lists;
 	}
 
 	/**
 	 * Get segments.
 	 *
+	 * @param array $args Array of search args.
+	 *
 	 * @return array|WP_Error List os existing segments or error.
 	 */
-	public function get_segments() {
-		$limit  = 100;
-		$offset = 0;
+	public function get_segments( $args = [] ) {
+		if ( null !== $this->segments ) {
+			if ( ! empty( $args['ids'] ) ) {
+				$filtered = array_values(
+					array_filter(
+						$this->segments,
+						function ( $segment ) use ( $args ) {
+							return Send_Lists::matches_id( $args['ids'], $segment['id'] );
+						}
+					)
+				);
+				return array_slice( $filtered, 0, $args['limit'] ?? count( $filtered ) );
+			}
+			if ( ! empty( $args['search'] ) ) {
+				$filtered = array_values(
+					array_filter(
+						$this->segments,
+						function ( $segment ) use ( $args ) {
+							return Send_Lists::matches_search( $args['search'], [ $segment['name'] ] );
+						}
+					)
+				);
+				return array_slice( $filtered, 0, $args['limit'] ?? count( $filtered ) );
+			}
+			return $this->segments;
+		}
+
+		$query_args           = $args;
+		$query_args['limit']  = $args['limit'] ?? 100;
+		$query_args['offset'] = 0;
 		$result = $this->api_v3_request(
 			'segments',
 			'GET',
 			[
-				'query' => [
-					'limit'  => $limit,
-					'offset' => $offset,
-				],
+				'query' => $query_args,
 			]
 		);
 		if ( is_wp_error( $result ) ) {
 			return $result;
 		}
 		$segments = $result['segments'];
-		$total    = $result['meta']['total'];
-		while ( $total > $offset + $limit ) {
-			$offset = $offset + $limit;
+		if ( isset( $args['limit'] ) ) {
+			return $segments;
+		}
+
+		// If not passed a limit, get all the segments.
+		$total = $result['meta']['total'];
+		while ( $total > $query_args['offset'] + $query_args['limit'] ) {
+			$query_args['offset'] = $query_args['offset'] + $query_args['limit'];
 			$result = $this->api_v3_request(
 				'segments',
 				'GET',
 				[
-					'query' => [
-						'limit'  => $limit,
-						'offset' => $offset,
-					],
+					'query' => $query_args,
 				]
 			);
 			if ( is_wp_error( $result ) ) {
@@ -553,7 +705,13 @@ public function get_segments() {
 			}
 			$segments = array_merge( $segments, $result['segments'] );
 		}
-		return $segments;
+
+		$this->segments = $segments;
+		if ( ! empty( $args['ids'] ) || ! empty( $args['search'] ) ) {
+			return $this->get_segments( $args );
+		}
+
+		return $this->segments;
 	}
 
 	/**
@@ -578,39 +736,81 @@ public function retrieve( $post_id, $skip_sync = false ) {
 		if ( ! $this->has_api_credentials() ) {
 			return [];
 		}
-		$lists = $this->get_lists();
-		if ( is_wp_error( $lists ) ) {
-			return $lists;
+
+		$campaign_id     = get_post_meta( $post_id, 'ac_campaign_id', true );
+		$send_list_id    = get_post_meta( $post_id, 'send_list_id', true );
+		$send_sublist_id = get_post_meta( $post_id, 'send_sublist_id', true );
+
+		// Handle legacy send-to meta.
+		if ( ! $send_list_id ) {
+			$legacy_list_id = get_post_meta( $post_id, 'ac_list_id', true );
+			if ( $legacy_list_id ) {
+				$newsletter_data['list_id'] = $legacy_list_id;
+				$send_list_id               = $legacy_list_id;
+			}
 		}
-		$segments = $this->get_segments();
-		if ( is_wp_error( $segments ) ) {
-			return $segments;
+		if ( ! $send_sublist_id ) {
+			$legacy_sublist_id = get_post_meta( $post_id, 'ac_segment_id', true );
+			if ( $legacy_sublist_id ) {
+				$newsletter_data['sublist_id'] = $legacy_sublist_id;
+				$send_sublist_id               = $legacy_sublist_id;
+			}
 		}
-		$campaign_id = get_post_meta( $post_id, 'ac_campaign_id', true );
-		$from_name   = get_post_meta( $post_id, 'ac_from_name', true );
-		$from_email  = get_post_meta( $post_id, 'ac_from_email', true );
-		$list_id     = get_post_meta( $post_id, 'ac_list_id', true );
-		$segment_id  = get_post_meta( $post_id, 'ac_segment_id', true );
-		$result      = [
-			'campaign'    => true, // Satisfy the JS API.
-			'campaign_id' => $campaign_id,
-			'from_name'   => $from_name,
-			'from_email'  => $from_email,
-			'list_id'     => $list_id,
-			'segment_id'  => $segment_id,
-			'lists'       => $lists,
-			'segments'    => $segments,
+		$send_lists = $this->get_send_lists( // Get first 10 top-level send lists for autocomplete.
+			[
+				'ids'  => $send_list_id ? [ $send_list_id ] : null, // If we have a selected list, make sure to fetch it.
+				'type' => 'list',
+			]
+		);
+		if ( is_wp_error( $send_lists ) ) {
+			return $send_lists;
+		}
+		$send_sublists = $send_list_id || $send_sublist_id ?
+			$this->get_send_lists(
+				[
+					'ids'       => [ $send_sublist_id ], // If we have a selected sublist, make sure to fetch it. Otherwise, we'll populate sublists later.
+					'parent_id' => $send_list_id,
+					'type'      => 'sublist',
+				]
+			) :
+			[];
+		if ( is_wp_error( $send_sublists ) ) {
+			return $send_sublists;
+		}
+		$newsletter_data = [
+			'campaign'                          => true, // Satisfy the JS API.
+			'campaign_id'                       => $campaign_id,
+			'supports_multiple_test_recipients' => true,
+			'lists'                             => $send_lists,
+			'sublists'                          => $send_sublists,
 		];
+
+		// Handle legacy sender meta.
+		$from_name   = get_post_meta( $post_id, 'senderName', true );
+		$from_email  = get_post_meta( $post_id, 'senderEmail', true );
+		if ( ! $from_name ) {
+			$legacy_from_name = get_post_meta( $post_id, 'ac_from_name', true );
+			if ( $legacy_from_name ) {
+				$newsletter_data['senderName'] = $legacy_from_name;
+			}
+		}
+		if ( ! $from_email ) {
+			$legacy_from_email = get_post_meta( $post_id, 'ac_from_email', true );
+			if ( $legacy_from_email ) {
+				$newsletter_data['senderEmail'] = $legacy_from_email;
+			}
+		}
+
 		if ( ! $campaign_id && true !== $skip_sync ) {
 			$sync_result = $this->sync( get_post( $post_id ) );
 			if ( ! is_wp_error( $sync_result ) ) {
-				$result = wp_parse_args(
+				$newsletter_data = wp_parse_args(
 					$sync_result,
-					$result
+					$newsletter_data
 				);
 			}
 		}
-		return $result;
+		return $newsletter_data;
 	}
 
 	/**
@@ -714,17 +914,19 @@ public function sync( $post ) {
 		$transient_name = $this->get_transient_name( $post->ID );
 		delete_transient( $transient_name );
 
-		$from_name  = get_post_meta( $post->ID, 'ac_from_name', true );
-		$from_email = get_post_meta( $post->ID, 'ac_from_email', true );
-		$list_id    = get_post_meta( $post->ID, 'ac_list_id', true );
-		$is_public  = get_post_meta( $post->ID, 'is_public', true );
-		$message_id = get_post_meta( $post->ID, 'ac_message_id', true );
+		$from_name    = get_post_meta( $post->ID, 'senderName', true );
+		$from_email   = get_post_meta( $post->ID, 'senderEmail', true );
+		$send_list_id = get_post_meta( $post->ID, 'send_list_id', true );
+		$message_id   = get_post_meta( $post->ID, 'ac_message_id', true );
 
 		$renderer = new Newspack_Newsletters_Renderer();
 		$content  = $renderer->retrieve_email_html( $post );
 
 		$message_action = 'message_add';
 		$message_data   = [];
+		$sync_data = [
+			'campaign' => true, // Satisfy JS API.
+		];
 
 		if ( $message_id ) {
 			$message = $this->api_v1_request( 'message_view', 'GET', [ 'query' => [ 'id' => $message_id ] ] );
@@ -736,10 +938,8 @@ public function sync( $post ) {
 
 			// If sender data is not available locally, update from ESP.
 			if ( ! $from_name || ! $from_email ) {
-				$from_name  = $message['fromname'];
-				$from_email = $message['fromemail'];
-				update_post_meta( $post->ID, 'ac_from_name', $from_name );
-				update_post_meta( $post->ID, 'ac_from_email', $from_email );
+				$sync_data['senderName']  = $message['fromname'];
+				$sync_data['senderEmail'] = $message['fromemail'];
 			}
 		} else {
 			// Validate required meta if campaign and message are not yet created.
@@ -749,7 +949,7 @@ public function sync( $post ) {
 					__( 'Please input sender name and email address.', 'newspack-newsletters' )
 				);
 			}
-			if ( empty( $list_id ) ) {
+			if ( empty( $send_list_id ) ) {
 				return new \WP_Error(
 					'newspack_newsletters_active_campaign_invalid_list',
 					__( 'Please select a list.', 'newspack-newsletters' )
@@ -759,13 +959,13 @@ public function sync( $post ) {
 
 		$message_data = wp_parse_args(
 			[
-				'format'              => 'html',
-				'htmlconstructor'     => 'editor',
-				'html'                => $content,
-				'p[' . $list_id . ']' => 1,
-				'fromemail'           => $from_email,
-				'fromname'            => $from_name,
-				'subject'             => $post->post_title,
+				'format'                   => 'html',
+				'htmlconstructor'          => 'editor',
+				'html'                     => $content,
+				'p[' . $send_list_id . ']' => 1,
+				'fromemail'                => $from_email,
+				'fromname'                 => $from_name,
+				'subject'                  => $post->post_title,
 			],
 			$message_data
 		);
@@ -776,14 +976,7 @@ public function sync( $post ) {
 		}
 
 		update_post_meta( $post->ID, 'ac_message_id', $message['id'] );
-
-		$sync_data = [
-			'campaign'   => true, // Satisfy JS API.
-			'message_id' => $message['id'],
-			'list_id'    => $list_id,
-			'from_email' => $from_email,
-			'from_name'  => $from_name,
-		];
+		$sync_data['message_id'] = $message['id'];
 
 		// Retrieve and store campaign data.
 		$data = $this->retrieve( $post->ID, true );
@@ -792,7 +985,6 @@ public function sync( $post ) {
 			return $data;
 		} else {
 			$data = array_merge( $data, $sync_data );
-			update_post_meta( $post->ID, 'newsletterData', $data );
 		}
 
 		return $sync_data;
@@ -811,8 +1003,13 @@ private function create_campaign( $post, $campaign_name = '' ) {
 		if ( is_wp_error( $sync_result ) ) {
 			return $sync_result;
 		}
-		$segment_id = get_post_meta( $post->ID, 'ac_segment_id', true );
-		$is_public  = get_post_meta( $post->ID, 'is_public', true );
+
+		$from_name       = get_post_meta( $post->ID, 'senderName', true );
+		$from_email      = get_post_meta( $post->ID, 'senderEmail', true );
+		$send_list_id    = get_post_meta( $post->ID, 'send_list_id', true );
+		$send_sublist_id = get_post_meta( $post->ID, 'send_sublist_id', true );
+
+		$is_public = get_post_meta( $post->ID, 'is_public', true );
 		if ( empty( $campaign_name ) ) {
 			$campaign_name = $this->get_campaign_name( $post );
 		}
@@ -821,10 +1018,10 @@ private function create_campaign( $post, $campaign_name = '' ) {
 			'status'                                => 0, // 0 = Draft; 1 = Scheduled.
 			'public'                                => (int) $is_public,
 			'name'                                  => $campaign_name,
-			'fromname'                              => $sync_result['from_name'],
-			'fromemail'                             => $sync_result['from_email'],
-			'segmentid'                             => $segment_id ?? 0, // 0 = No segment.
-			'p[' . $sync_result['list_id'] . ']'    => $sync_result['list_id'],
+			'fromname'                              => $from_name,
+			'fromemail'                             => $from_email,
+			'segmentid'                             => $send_sublist_id ?? 0, // 0 = No segment.
+			'p[' . $send_list_id . ']'              => $send_list_id,
 			'm[' . $sync_result['message_id'] . ']' => 100, // 100 = 100% of contacts will receive this.
 		];
 		if ( defined( 'NEWSPACK_NEWSLETTERS_AC_DISABLE_LINK_TRACKING' ) && NEWSPACK_NEWSLETTERS_AC_DISABLE_LINK_TRACKING ) {
@@ -1335,6 +1532,12 @@ public static function get_labels( $context = '' ) {
 				'name'                   => 'Active Campaign',
 				'list_explanation'       => __( 'Active Campaign List', 'newspack-newsletters' ),
 				'local_list_explanation' => __( 'Active Campaign Tag', 'newspack-newsletters' ),
+				'list'                   => __( 'list', 'newspack-newsletters' ), // "list" in lower case singular format.
+				'lists'                  => __( 'lists', 'newspack-newsletters' ), // "list" in lower case plural format.
+				'sublist'                => __( 'segment', 'newspack-newsletters' ), // Sublist entities in lowercase singular format.
+				'List'                   => __( 'List', 'newspack-newsletters' ), // "list" in uppercase case singular format.
+				'Lists'                  => __( 'Lists', 'newspack-newsletters' ), // "list" in uppercase case plural format.
+				'Sublist'                => __( 'Segments', 'newspack-newsletters' ), // Sublist entities in uppercase singular format.
 			]
 		);
 	}
diff --git a/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor-controller.php b/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor-controller.php
index dabce22ea..ba25966fe 100644
--- a/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor-controller.php
+++ b/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor-controller.php
@@ -18,107 +18,10 @@ class Newspack_Newsletters_Campaign_Monitor_Controller extends Newspack_Newslett
 	 */
 	public function __construct( $campaign_monitor ) {
 		$this->service_provider = $campaign_monitor;
-		add_action( 'init', [ __CLASS__, 'register_meta' ] );
 		add_action( 'rest_api_init', [ $this, 'register_routes' ] );
 		parent::__construct( $campaign_monitor );
 	}
 
-	/**
-	 * Register custom fields.
-	 */
-	public static function register_meta() {
-		\register_meta(
-			'post',
-			'cm_list_id',
-			[
-				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
-				'type'           => 'string',
-				'single'         => true,
-				'auth_callback'  => '__return_true',
-			]
-		);
-		\register_meta(
-			'post',
-			'cm_segment_id',
-			[
-				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
-				'type'           => 'string',
-				'single'         => true,
-				'auth_callback'  => '__return_true',
-			]
-		);
-		\register_meta(
-			'post',
-			'cm_send_mode',
-			[
-				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
-				'type'           => 'string',
-				'single'         => true,
-				'auth_callback'  => '__return_true',
-			]
-		);
-		\register_meta(
-			'post',
-			'cm_from_name',
-			[
-				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
-				'type'           => 'string',
-				'single'         => true,
-				'auth_callback'  => '__return_true',
-			]
-		);
-		\register_meta(
-			'post',
-			'cm_from_email',
-			[
-				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
-				'type'           => 'string',
-				'single'         => true,
-				'auth_callback'  => '__return_true',
-			]
-		);
-		\register_meta(
-			'post',
-			'cm_preview_text',
-			[
-				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
-				'type'           => 'string',
-				'single'         => true,
-				'auth_callback'  => '__return_true',
-			]
-		);
-	}
-
 	/**
 	 * Register API endpoints unique to Campaign Monitor.
 	 */
@@ -134,7 +37,7 @@ public function register_routes() {
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ $this, 'api_retrieve' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id' => [
 						'sanitize_callback' => 'absint',
@@ -143,22 +46,13 @@ public function register_routes() {
 				],
 			]
 		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<public_id>[\a-z]+)/content',
-			[
-				'methods'             => \WP_REST_Server::READABLE,
-				'callback'            => [ $this, 'api_content' ],
-				'permission_callback' => '__return_true',
-			]
-		);
 		\register_rest_route(
 			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
 			'(?P<id>[\a-z]+)/test',
 			[
 				'methods'             => \WP_REST_Server::EDITABLE,
 				'callback'            => [ $this, 'api_test' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id'         => [
 						'sanitize_callback' => 'absint',
@@ -201,25 +95,4 @@ public function api_test( $request ) {
 		);
 		return self::get_api_response( $response );
 	}
-
-	/**
-	 * Get raw HTML for a campaign. Required for the Campaign Monitor API.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return void|WP_Error
-	 */
-	public function api_content( $request ) {
-		$response = $this->service_provider->content(
-			$request['public_id']
-		);
-
-		if ( is_wp_error( $response ) ) {
-			return self::get_api_response( $response );
-		}
-
-		header( 'Content-Type: text/html; charset=UTF-8' );
-
-		echo $response; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
-		exit();
-	}
 }
diff --git a/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor.php b/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor.php
index ada28dfe9..ddd901811 100644
--- a/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor.php
+++ b/includes/service-providers/campaign_monitor/class-newspack-newsletters-campaign-monitor.php
@@ -7,6 +7,9 @@
 
 defined( 'ABSPATH' ) || exit;
 
+use Newspack\Newsletters\Send_Lists;
+use Newspack\Newsletters\Send_List;
+
 // Increase default timeout for 3rd-party API requests to 30s.
 define( 'CS_REST_CALL_TIMEOUT', 30 );
 
@@ -22,6 +25,21 @@ final class Newspack_Newsletters_Campaign_Monitor extends \Newspack_Newsletters_
 	 */
 	public $name = 'Campaign Monitor';
 
+	/**
+	 * Cached lists.
+	 *
+	 * @var array
+	 */
+	private $lists = null;
+
+	/**
+	 * Cached segments.
+	 *
+	 * @var array
+	 */
+	private $segments = null;
+
+
 	/**
 	 * Class constructor.
 	 */
@@ -115,9 +133,13 @@ public function set_api_credentials( $credentials ) {
 	/**
 	 * Get lists for a client iD.
 	 *
-	 * @return object|WP_Error API API Response or error.
+	 * @return array|WP_Error Array of lists, or error.
 	 */
 	public function get_lists() {
+		if ( null !== $this->lists ) {
+			return $this->lists;
+		}
+
 		$api_key   = $this->api_key();
 		$client_id = $this->client_id();
 
@@ -145,7 +167,7 @@ public function get_lists() {
 			);
 		}
 
-		return array_map(
+		$lists = array_map(
 			function ( $item ) {
 				return [
 					'id'   => $item->ListID, // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
@@ -154,14 +176,21 @@ function ( $item ) {
 			},
 			$lists->response
 		);
+
+		$this->lists = $lists;
+		return $this->lists;
 	}
 
 	/**
 	 * Get segments for a client iD.
 	 *
-	 * @return object|WP_Error API API Response or error.
+	 * @return array|WP_Error Array of segments, or error.
 	 */
 	public function get_segments() {
+		if ( null !== $this->segments ) {
+			return $this->segments;
+		}
+
 		$api_key   = $this->api_key();
 		$client_id = $this->client_id();
 
@@ -189,46 +218,182 @@ public function get_segments() {
 			);
 		}
 
-		return $segments->response;
+		$segments = array_map(
+			function ( $item ) {
+				return [
+					'id'     => $item->SegmentID, // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
+					'name'   => $item->Title, // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
+					'parent' => $item->ListID, // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
+				];
+			},
+			$segments->response
+		);
+
+		$this->segments = $segments;
+		return $this->segments;
+	}
+
+	/**
+	 * Get all applicable lists and segments as Send_List objects.
+	 * Note that in CM, campaigns can be sent to either lists or segments, not both,
+	 * so both entity types should be treated as top-level send lists.
+	 *
+	 * @param array $args Array of search args. See Send_Lists::get_default_args() for supported params and default values.
+	 *
+	 * @return Send_List[]|WP_Error Array of Send_List objects on success, or WP_Error object on failure.
+	 */
+	public function get_send_lists( $args = [] ) {
+		$api_key   = $this->api_key();
+		$client_id = $this->client_id();
+
+		if ( ! $api_key ) {
+			return new WP_Error(
+				'newspack_newsletters_missing_api_key',
+				__( 'No Campaign Monitor API key available.', 'newspack-newsletters' )
+			);
+		}
+		if ( ! $client_id ) {
+			return new WP_Error(
+				'newspack_newsletters_missing_client_id',
+				__( 'No Campaign Monitor Client ID available.', 'newspack-newsletters' )
+			);
+		}
+
+		$lists = $this->get_lists();
+		if ( is_wp_error( $lists ) ) {
+			return $lists;
+		}
+		$send_lists = array_map(
+			function( $list ) use ( $api_key ) {
+				$config = [
+					'provider'    => $this->service,
+					'type'        => 'list',
+					'id'          => $list['id'],
+					'name'        => $list['name'],
+					'entity_type' => 'list',
+				];
+
+				$list_details = new CS_REST_Lists( $list['id'], [ 'api_key' => $api_key ] );
+				$list_stats   = $list_details->get_stats();
+				if ( ! empty( $list_stats->response->TotalActiveSubscribers ) ) {
+					$config['count'] = $list_stats->response->TotalActiveSubscribers;
+				}
+
+				return new Send_List( $config );
+			},
+			$lists
+		);
+		$segments = $this->get_segments();
+		if ( is_wp_error( $segments ) ) {
+			return $segments;
+		}
+		$send_segments = array_map(
+			function( $segment ) {
+				$segment_id = (string) $segment['id'];
+				$config      = [
+					'provider'    => $this->service,
+					'type'        => 'list', // In CM, segments and lists have the same hierarchy.
+					'id'          => $segment_id,
+					'name'        => $segment['name'],
+					'entity_type' => 'segment',
+				];
+
+				return new Send_List( $config );
+			},
+			$segments
+		);
+		$send_lists    = array_merge( $send_lists, $send_segments );
+		$filtered_lists = $send_lists;
+		if ( ! empty( $args['ids'] ) ) {
+			$ids           = ! is_array( $args['ids'] ) ? [ $args['ids'] ] : $args['ids'];
+			$filtered_lists = array_values(
+				array_filter(
+					$send_lists,
+					function ( $list ) use ( $ids ) {
+						return Send_Lists::matches_id( $ids, $list->get_id() );
+					}
+				)
+			);
+		}
+		if ( ! empty( $args['search'] ) ) {
+			$search        = ! is_array( $args['search'] ) ? [ $args['search'] ] : $args['search'];
+			$filtered_lists = array_values(
+				array_filter(
+					$send_lists,
+					function ( $list ) use ( $search ) {
+						return Send_Lists::matches_search(
+							$search,
+							[
+								$list->get_id(),
+								$list->get_name(),
+								$list->get_entity_type(),
+							]
+						);
+					}
+				)
+			);
+		}
+
+		if ( ! empty( $args['limit'] ) ) {
+			$filtered_lists = array_slice( $filtered_lists, 0, $args['limit'] );
+		}
+
+		return $filtered_lists;
 	}
 
 	/**
 	 * Retrieve campaign details.
 	 *
 	 * @param integer $post_id Numeric ID of the Newsletter post.
-	 * @param boolean $fetch_all If true, returns all campaign data, even those stored in WP.
 	 * @return object|WP_Error API Response or error.
+	 * @throws Exception Error message.
 	 */
-	public function retrieve( $post_id, $fetch_all = false ) {
+	public function retrieve( $post_id ) {
 		if ( ! $this->has_api_credentials() ) {
 			return [];
 		}
 		try {
-			$cm       = new CS_REST_General( $this->api_key() );
-			$response = [];
-
-			$lists    = $this->get_lists();
-			$segments = $this->get_segments();
-
-			$response['lists']    = ! empty( $lists ) ? $lists : [];
-			$response['segments'] = ! empty( $segments ) ? $segments : [];
-
-			if ( $fetch_all ) {
-				$cm_send_mode  = $this->retrieve_send_mode( $post_id );
-				$cm_list_id    = $this->retrieve_list_id( $post_id );
-				$cm_segment_id = $this->retrieve_segment_id( $post_id );
-				$cm_from_name  = $this->retrieve_from_name( $post_id );
-				$cm_from_email = $this->retrieve_from_email( $post_id );
-
-				$response['send_mode']  = $cm_send_mode;
-				$response['list_id']    = $cm_list_id;
-				$response['segment_id'] = $cm_segment_id;
-				$response['from_name']  = $cm_from_name;
-				$response['from_email'] = $cm_from_email;
-				$response['campaign']   = true;
+			$send_list_id    = get_post_meta( $post_id, 'send_list_id', true );
+			$send_lists      = $this->get_send_lists( // Get first 10 top-level send lists for autocomplete.
+				[
+					'ids'  => $send_list_id ? [ $send_list_id ] : null, // If we have a selected list, make sure to fetch it.
+					'type' => 'list',
+				]
+			);
+			if ( is_wp_error( $send_lists ) ) {
+				throw new Exception( wp_kses_post( $send_lists->get_error_message() ) );
+			}
+			$newsletter_data = [
+				'campaign'                          => true, // Satisfy the JS API.
+				'supports_multiple_test_recipients' => true,
+				'lists'                             => $send_lists,
+			];
+
+			// Handle legacy sender meta.
+			$from_name   = get_post_meta( $post_id, 'senderName', true );
+			$from_email  = get_post_meta( $post_id, 'senderEmail', true );
+			if ( ! $from_name ) {
+				$legacy_from_name = get_post_meta( $post_id, 'cm_from_name', true );
+				if ( $legacy_from_name ) {
+					$newsletter_data['senderName'] = $legacy_from_name;
+				}
+			}
+			if ( ! $from_email ) {
+				$legacy_from_email = get_post_meta( $post_id, 'cm_from_email', true );
+				if ( $legacy_from_email ) {
+					$newsletter_data['senderEmail'] = $legacy_from_email;
+				}
 			}
 
-			return $response;
+			// Handle legacy send-to meta.
+			if ( ! $send_list_id ) {
+				$legacy_list_id = get_post_meta( $post_id, 'cm_list_id', true ) ?? get_post_meta( $post_id, 'cm_segment_id', true );
+				if ( $legacy_list_id ) {
+					$newsletter_data['list_id'] = $legacy_list_id;
+				}
+			}
+
+			return $newsletter_data;
 		} catch ( Exception $e ) {
 			return new WP_Error(
 				'newspack_newsletters_campaign_monitor_error',
@@ -276,20 +441,20 @@ public function test( $post_id, $emails ) {
 			}
 
 			// Use the temporary test campaign ID to send a preview.
-			$preview = new CS_REST_Campaigns( $test_campaign->response, [ 'api_key' => $api_key ] );
-			$preview->send_preview( $emails );
+			$preview          = new CS_REST_Campaigns( $test_campaign->response, [ 'api_key' => $api_key ] );
+			$preview_response = $preview->send_preview( $emails );
 
 			// After sending a preview, delete the temporary test campaign. We must do this because the API doesn't support updating campaigns.
-			$delete = $preview->delete();
-
-			$data['result']  = $test_campaign->response;
-			$data['message'] = sprintf(
-			// translators: Message after successful test email.
-				__( 'Campaign Monitor test sent successfully to %s.', 'newspack-newsletters' ),
-				implode( ', ', $emails )
-			);
-
-			return \rest_ensure_response( $data );
+			$deleted  = $preview->delete();
+			$response = [
+				'result'  => $preview_response->response,
+				'message' => sprintf(
+					// translators: Message after successful test email.
+					__( 'Campaign Monitor test sent successfully to %s.', 'newspack-newsletters' ),
+					implode( ', ', $emails )
+				),
+			];
+			return \rest_ensure_response( $response );
 		} catch ( Exception $e ) {
 			return new WP_Error(
 				'newspack_newsletters_campaign_monitor_error',
@@ -305,7 +470,6 @@ public function test( $post_id, $emails ) {
 	 * @return object Args for sending a campaign or campaign preview.
 	 */
 	public function format_campaign_args( $post_id ) {
-		$data      = $this->validate( $this->retrieve( $post_id, true ) );
 		$public_id = get_post_meta( $post_id, Newspack_Newsletters::PUBLIC_POST_ID_META, true );
 
 		// If we don't have a public ID, generate one and save it.
@@ -317,18 +481,25 @@ public function format_campaign_args( $post_id ) {
 		$args = [
 			'Subject'   => get_the_title( $post_id ),
 			'Name'      => get_the_title( $post_id ) . ' ' . gmdate( 'h:i:s A' ), // Name must be unique.
-			'FromName'  => $data['from_name'],
-			'FromEmail' => $data['from_email'],
-			'ReplyTo'   => $data['from_email'],
+			'FromName'  => get_post_meta( $post_id, 'senderName', true ),
+			'FromEmail' => get_post_meta( $post_id, 'senderEmail', true ),
+			'ReplyTo'   => get_post_meta( $post_id, 'senderEmail', true ),
 			'HtmlUrl'   => rest_url(
 				$this::BASE_NAMESPACE . $this->service . '/' . $public_id . '/content'
 			),
 		];
 
-		if ( 'list' === $data['send_mode'] ) {
-			$args['ListIDs'] = [ $data['list_id'] ];
-		} else {
-			$args['SegmentIDs'] = [ $data['segment_id'] ];
+		$send_list_id = get_post_meta( $post_id, 'send_list_id', true );
+		if ( $send_list_id ) {
+			$send_list = $this->get_send_lists( [ 'ids' => $send_list_id ] );
+			if ( ! empty( $send_list[0] ) ) {
+				$send_mode = $send_list[0]->get_entity_type();
+				if ( 'list' === $send_mode ) {
+					$args['ListIDs'] = [ $send_list_id ];
+				} elseif ( 'segment' === $send_mode ) {
+					$args['SegmentIDs'] = [ $send_list_id ];
+				}
+			}
 		}
 
 		return $args;
@@ -688,7 +859,11 @@ public static function get_labels( $context = '' ) {
 		return array_merge(
 			parent::get_labels(),
 			[
-				'name' => 'Campaign Monitor',
+				'name'  => 'Campaign Monitor',
+				'list'  => __( 'list or segment', 'newspack-newsletters' ), // "list" in lower case singular format.
+				'lists' => __( 'lists or segments', 'newspack-newsletters' ), // "list" in lower case plural format.
+				'List'  => __( 'List or Segment', 'newspack-newsletters' ), // "list" in uppercase case singular format.
+				'Lists' => __( 'Lists or Segments', 'newspack-newsletters' ), // "list" in uppercase case plural format.
 			]
 		);
 	}
diff --git a/includes/service-providers/class-newspack-newsletters-service-provider-controller.php b/includes/service-providers/class-newspack-newsletters-service-provider-controller.php
index dd3ebd95d..6ddbca6d5 100644
--- a/includes/service-providers/class-newspack-newsletters-service-provider-controller.php
+++ b/includes/service-providers/class-newspack-newsletters-service-provider-controller.php
@@ -17,7 +17,7 @@ abstract class Newspack_Newsletters_Service_Provider_Controller extends \WP_REST
 	 *
 	 * @var Newspack_Newsletters_Service_Provider $service_provider
 	 */
-	private $service_provider;
+	protected $service_provider;
 
 	/**
 	 * Newspack_Newsletters_Service_Provider_Controller constructor.
@@ -33,12 +33,12 @@ public function __construct( $service_provider ) {
 	 */
 	public function register_routes() {
 		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE,
+			Newspack_Newsletters::API_NAMESPACE,
 			'(?P<id>[\a-z]+)/sync-error',
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ $this, 'api_get_sync_error' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id' => [
 						'sanitize_callback' => 'absint',
diff --git a/includes/service-providers/class-newspack-newsletters-service-provider.php b/includes/service-providers/class-newspack-newsletters-service-provider.php
index 236687cd6..ef659aa13 100644
--- a/includes/service-providers/class-newspack-newsletters-service-provider.php
+++ b/includes/service-providers/class-newspack-newsletters-service-provider.php
@@ -94,25 +94,6 @@ public static function instance() {
 		return self::$instances[ static::class ];
 	}
 
-	/**
-	 * Check capabilities for using the API for authoring tasks.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return bool|WP_Error
-	 */
-	public function api_authoring_permissions_check( $request ) {
-		if ( ! current_user_can( 'edit_others_posts' ) ) {
-			return new \WP_Error(
-				'newspack_rest_forbidden',
-				esc_html__( 'You cannot use this resource.', 'newspack-newsletters' ),
-				[
-					'status' => 403,
-				]
-			);
-		}
-		return true;
-	}
-
 	/**
 	 * Handle newsletter post status changes.
 	 *
@@ -448,8 +429,10 @@ public static function get_labels( $context = '' ) {
 			'name'                    => '', // The provider name.
 			'list'                    => __( 'list', 'newspack-newsletters' ), // "list" in lower case singular format.
 			'lists'                   => __( 'lists', 'newspack-newsletters' ), // "list" in lower case plural format.
+			'sublist'                 => __( 'sublist', 'newspack-newsletters' ), // Sublist entities in lowercase singular format.
 			'List'                    => __( 'List', 'newspack-newsletters' ), // "list" in uppercase case singular format.
 			'Lists'                   => __( 'Lists', 'newspack-newsletters' ), // "list" in uppercase case plural format.
+			'Sublist'                 => __( 'Sublist', 'newspack-newsletters' ), // Sublist entities in uppercase singular format.
 			'tag_prefix'              => 'Newspack: ', // The prefix to be used in tags.
 			'tag_metabox_before_save' => __( 'Once this list is saved, a tag will be created for it.', 'newspack-newsletters' ),
 			'tag_metabox_after_save'  => __( 'Tag created for this list', 'newspack-newsletters' ),
diff --git a/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-controller.php b/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-controller.php
index 6c6cd326a..02c76b877 100644
--- a/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-controller.php
+++ b/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-controller.php
@@ -54,7 +54,7 @@ public function register_routes() {
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ $this, 'verify_token' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 			]
 		);
 		\register_rest_route(
@@ -63,7 +63,7 @@ public function register_routes() {
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ $this, 'api_retrieve' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id' => [
 						'sanitize_callback' => 'absint',
@@ -78,7 +78,7 @@ public function register_routes() {
 			[
 				'methods'             => \WP_REST_Server::EDITABLE,
 				'callback'            => [ $this, 'api_test' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id'         => [
 						'sanitize_callback' => 'absint',
@@ -90,99 +90,6 @@ public function register_routes() {
 				],
 			]
 		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/sender',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_sender' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'        => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'from_name' => [
-						'sanitize_callback' => 'sanitize_text_field',
-					],
-					'reply_to'  => [
-						'sanitize_callback' => 'sanitize_email',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/list/(?P<list_id>[\a-z]+)',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_list' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'      => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'list_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/list/(?P<list_id>[\a-z]+)',
-			[
-				'methods'             => \WP_REST_Server::DELETABLE,
-				'callback'            => [ $this, 'api_list' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'      => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'list_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/segment/(?P<segment_id>[\a-z]+)',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_segment' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'         => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'segment_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/segment/',
-			[
-				'methods'             => \WP_REST_Server::DELETABLE,
-				'callback'            => [ $this, 'api_segment' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'         => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'segment_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
 	}
 
 	/**
@@ -224,60 +131,4 @@ public function api_test( $request ) {
 		);
 		return self::get_api_response( $response );
 	}
-
-	/**
-	 * Set the sender name and email for the campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_sender( $request ) {
-		$response = $this->service_provider->sender(
-			$request['id'],
-			$request['from_name'],
-			$request['reply_to']
-		);
-		return self::get_api_response( $response );
-	}
-
-	/**
-	 * Set list for a campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_list( $request ) {
-		if ( 'DELETE' === $request->get_method() ) {
-			$response = $this->service_provider->unset_list(
-				$request['id'],
-				$request['list_id']
-			);
-		} else {
-			$response = $this->service_provider->list(
-				$request['id'],
-				$request['list_id']
-			);
-		}
-		return self::get_api_response( $response );
-	}
-
-	/**
-	 * Set segment for a campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_segment( $request ) {
-		if ( 'DELETE' === $request->get_method() ) {
-			$response = $this->service_provider->unset_segment(
-				$request['id']
-			);
-		} else {
-			$response = $this->service_provider->set_segment(
-				$request['id'],
-				$request['segment_id']
-			);
-		}
-		return self::get_api_response( $response );
-	}
 }
diff --git a/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-sdk.php b/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-sdk.php
index 99a3b88f7..83c86aab8 100644
--- a/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-sdk.php
+++ b/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact-sdk.php
@@ -294,10 +294,12 @@ public function get_account_info() {
 	/**
 	 * Get account email addresses
 	 *
+	 * @param array $args Array of query args.
+	 *
 	 * @return object Email addresses.
 	 */
-	public function get_email_addresses() {
-		return $this->request( 'GET', 'account/emails' );
+	public function get_email_addresses( $args = [] ) {
+		return $this->request( 'GET', 'account/emails', [ 'query' => $args ] );
 	}
 
 	/**
@@ -306,26 +308,68 @@ public function get_email_addresses() {
 	 * @return object Contact lists.
 	 */
 	public function get_contact_lists() {
+		$args = [
+			'include_count'            => 'true',
+			'include_membership_count' => 'active',
+			'limit'                    => 1000,
+			'status'                   => 'active',
+		];
 		return $this->request(
 			'GET',
 			'contact_lists',
-			[ 'query' => [ 'include_count' => 'true' ] ]
+			[ 'query' => $args ]
 		)->lists;
 	}
 
+	/**
+	 * Get a Contact List by ID
+	 *
+	 * @param string $id Contact List ID.
+	 *
+	 * @return object Contact list.
+	 */
+	public function get_contact_list( $id ) {
+		$args = [
+			'include_membership_count' => 'active',
+		];
+		return $this->request(
+			'GET',
+			'contact_lists/' . $id,
+			[ 'query' => $args ]
+		);
+	}
+
 	/**
 	 * Get segments
 	 *
 	 * @return array
 	 */
 	public function get_segments() {
+		$args = [
+			'limit'   => 1000,
+			'sort_by' => 'date',
+		];
 		return $this->request(
 			'GET',
 			'segments',
-			[ 'query' => [ 'sort_by' => 'name' ] ]
+			[ 'query' => $args ]
 		)->segments;
 	}
 
+	/**
+	 * Get a segment by ID
+	 *
+	 * @param string $id Segment ID.
+	 *
+	 * @return object Segment.
+	 */
+	public function get_segment( $id ) {
+		return $this->request(
+			'GET',
+			'segments/' . $id
+		);
+	}
+
 	/**
 	 * Get v3 campaign UUID if matches v2 format.
 	 *
diff --git a/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact.php b/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact.php
index 86ecd266c..a7b6e404d 100644
--- a/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact.php
+++ b/includes/service-providers/constant_contact/class-newspack-newsletters-constant-contact.php
@@ -7,11 +7,28 @@
 
 defined( 'ABSPATH' ) || exit;
 
+use Newspack\Newsletters\Send_Lists;
+use Newspack\Newsletters\Send_List;
+
 /**
  * Main Newspack Newsletters Class for Constant Contact ESP.
  */
 final class Newspack_Newsletters_Constant_Contact extends \Newspack_Newsletters_Service_Provider {
 
+	/**
+	 * Provider name.
+	 *
+	 * @var string
+	 */
+	public $name = 'Contant Constact';
+
+	/**
+	 * Cached instance of the CC SDK.
+	 *
+	 * @var Newspack_Newsletters_Constant_Contact_SDK
+	 */
+	private $cc = null;
+
 	/**
 	 * Cached lists.
 	 *
@@ -20,18 +37,18 @@ final class Newspack_Newsletters_Constant_Contact extends \Newspack_Newsletters_
 	private $lists = null;
 
 	/**
-	 * Cached contact data.
+	 * Cached segments.
 	 *
 	 * @var array
 	 */
-	private $contact_data = [];
+	private $segments = null;
 
 	/**
-	 * Provider name.
+	 * Cached contact data.
 	 *
-	 * @var string
+	 * @var array
 	 */
-	public $name = 'Contant Constact';
+	private $contact_data = [];
 
 	/**
 	 * Whether the provider has support to tags and tags based Subscription Lists.
@@ -46,6 +63,7 @@ final class Newspack_Newsletters_Constant_Contact extends \Newspack_Newsletters_
 	public function __construct() {
 		$this->service    = 'constant_contact';
 		$this->controller = new Newspack_Newsletters_Constant_Contact_Controller( $this );
+		$credentials      = $this->api_credentials();
 
 		add_action( 'admin_init', [ $this, 'oauth_callback' ] );
 		add_action( 'update_option_newspack_newsletters_constant_contact_api_key', [ $this, 'clear_tokens' ], 10, 2 );
@@ -79,6 +97,22 @@ public function has_api_credentials() {
 		return ! empty( $this->api_key() ) && ! empty( $this->api_secret() );
 	}
 
+	/**
+	 * Get or create a cached instance of the Constant Contact SDK.
+	 */
+	public function get_sdk() {
+		if ( $this->cc ) {
+			return $this->cc;
+		}
+		$credentials = $this->api_credentials();
+		$this->cc    = new Newspack_Newsletters_Constant_Contact_SDK(
+			$credentials['api_key'],
+			$credentials['api_secret'],
+			$credentials['access_token']
+		);
+		return $this->cc;
+	}
+
 	/**
 	 * Verify service provider connection.
 	 *
@@ -88,15 +122,9 @@ public function has_api_credentials() {
 	 */
 	public function verify_token( $refresh = true ) {
 		try {
-			$credentials  = $this->api_credentials();
 			$redirect_uri = $this->get_oauth_redirect_uri();
-			$cc           = new Newspack_Newsletters_Constant_Contact_SDK(
-				$credentials['api_key'],
-				$credentials['api_secret'],
-				$credentials['access_token']
-			);
-
-			$response = [
+			$cc           = $this->get_sdk();
+			$response     = [
 				'error'    => null,
 				'valid'    => false,
 				'auth_url' => $cc->get_auth_code_url( wp_create_nonce( 'constant_contact_oauth2' ), $redirect_uri ),
@@ -106,7 +134,9 @@ public function verify_token( $refresh = true ) {
 				$response['valid'] = true;
 				return $response;
 			}
+
 			// If we have a refresh token, we can get a new access token.
+			$credentials = $this->api_credentials();
 			if ( $refresh && ! empty( $credentials['refresh_token'] ) ) {
 				$token             = $cc->refresh_token( $credentials['refresh_token'] );
 				$response['valid'] = $this->set_access_token( $token->access_token, $token->refresh_token );
@@ -189,7 +219,7 @@ public function oauth_callback() {
 	 * @return boolean Whether we are connected.
 	 */
 	private function connect( $redirect_uri, $code ) {
-		$cc    = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret() );
+		$cc    = $this->get_sdk();
 		$token = $cc->get_access_token( $redirect_uri, $code );
 		if ( ! $token || ! isset( $token->access_token ) ) {
 			return false;
@@ -306,7 +336,7 @@ public function list( $post_id, $list_id ) {
 		}
 		try {
 			$cc_campaign_id = $this->retrieve_campaign_id( $post_id );
-			$cc             = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc             = $this->get_sdk();
 
 			$campaign = $cc->get_campaign( $cc_campaign_id );
 			$activity = $campaign->activity;
@@ -344,7 +374,7 @@ public function unset_list( $post_id, $list_id ) {
 		}
 		try {
 			$cc_campaign_id = $this->retrieve_campaign_id( $post_id );
-			$cc             = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc             = $this->get_sdk();
 
 			$campaign = $cc->get_campaign( $cc_campaign_id );
 			$activity = $campaign->activity;
@@ -381,7 +411,7 @@ public function set_segment( $post_id, $segment_id ) {
 		}
 		try {
 			$cc_campaign_id = $this->retrieve_campaign_id( $post_id );
-			$cc             = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc             = $this->get_sdk();
 
 			$campaign = $cc->get_campaign( $cc_campaign_id );
 			$activity = $campaign->activity;
@@ -418,7 +448,7 @@ public function unset_segment( $post_id ) {
 		}
 		try {
 			$cc_campaign_id = $this->retrieve_campaign_id( $post_id );
-			$cc             = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc             = $this->get_sdk();
 
 			$campaign = $cc->get_campaign( $cc_campaign_id );
 			$activity = $campaign->activity;
@@ -442,13 +472,14 @@ public function unset_segment( $post_id ) {
 	 *
 	 * @param integer $post_id Numeric ID of the Newsletter post.
 	 * @return object|WP_Error API Response or error.
+	 * @throws Exception Error message.
 	 */
 	public function retrieve( $post_id ) {
 		if ( ! $this->has_api_credentials() || ! $this->has_valid_connection() ) {
 			return [];
 		}
 		try {
-			$cc             = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc             = $this->get_sdk();
 			$cc_campaign_id = get_post_meta( $post_id, 'cc_campaign_id', true );
 
 			if ( ! $cc_campaign_id ) {
@@ -458,21 +489,46 @@ public function retrieve( $post_id ) {
 				$campaign = $cc->get_campaign( $cc_campaign_id );
 			}
 
-			$lists    = $cc->get_contact_lists();
-			$segments = $cc->get_segments();
-
-			$data = [
-				'lists'       => $lists,
-				'campaign'    => $campaign,
-				'campaign_id' => $cc_campaign_id,
-				'segments'    => $segments,
+			$list_id         = $campaign->activity->contact_list_ids[0] ?? null;
+			$segment_id      = $campaign->activity->segment_ids[0] ?? null;
+			$send_list_id    = get_post_meta( $post_id, 'send_list_id', true );
+			$newsletter_data = [
+				'campaign'              => $campaign,
+				'campaign_id'           => $cc_campaign_id,
+				'allowed_sender_emails' => $this->get_verified_email_addresses(), // Get allowed email addresses for sender UI.
+				'email_settings_url'    => 'https://app.constantcontact.com/pages/myaccount/settings/emails',
 			];
 
-			// Store retrieved campaign data.
-			update_post_meta( $post_id, 'newsletterData', $data );
+			// Reconcile campaign settings with info fetched from the ESP for a true two-way sync.
+			if ( ! empty( $campaign->activity->from_name ) && $campaign->activity->from_name !== get_post_meta( $post_id, 'senderName', true ) ) {
+				$newsletter_data['senderName'] = $campaign->activity->from_name; // If campaign has different sender info set, update ours.
+			}
+			if ( ! empty( $campaign->activity->from_email ) && $campaign->activity->from_email !== get_post_meta( $post_id, 'senderEmail', true ) ) {
+				$newsletter_data['senderEmail'] = $campaign->activity->from_email; // If campaign has different sender info set, update ours.
+			}
+			if ( ( $list_id || $segment_id ) && $list_id !== $send_list_id && $segment_id !== $send_list_id ) {
+				$newsletter_data['send_list_id'] = strval( $list_id ?? $segment_id ); // If campaign has different list or segment set, update ours.
+				$send_list_id                    = $newsletter_data['send_list_id'];
+			}
+
+			// Prefetch send list info if we have a selected list and/or sublist.
+			$send_lists = $this->get_send_lists(
+				[
+					'ids'  => $send_list_id ? [ $send_list_id ] : null, // If we have a selected list, make sure to fetch it.
+					'type' => 'list',
+				]
+			);
+			if ( is_wp_error( $send_lists ) ) {
+				throw new Exception( wp_kses_post( $send_lists->get_error_message() ) );
+			}
+			$newsletter_data['lists'] = $send_lists;
 
-			return $data;
+			return $newsletter_data;
 		} catch ( Exception $e ) {
+			// If we couldn't get the campaign, delete the cc_campaign_id so it gets recreated on the next sync.
+			delete_post_meta( $post_id, 'cc_campaign_id' );
+			$this->retrieve( $post_id );
+
 			return new WP_Error(
 				'newspack_newsletters_constant_contact_error',
 				$e->getMessage()
@@ -498,7 +554,7 @@ public function sender( $post_id, $from_name, $reply_to ) {
 		try {
 			$post           = get_post( $post_id );
 			$cc_campaign_id = $this->retrieve_campaign_id( $post_id );
-			$cc             = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc             = $this->get_sdk();
 			$renderer       = new Newspack_Newsletters_Renderer();
 			$content        = $renderer->retrieve_email_html( $post );
 
@@ -540,8 +596,7 @@ public function test( $post_id, $emails ) {
 			);
 		}
 		try {
-			$cc = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
-
+			$cc   = $this->get_sdk();
 			$data = $this->retrieve( $post_id );
 
 			if ( is_wp_error( $data ) ) {
@@ -567,6 +622,86 @@ public function test( $post_id, $emails ) {
 		}
 	}
 
+	/**
+	 * Get all of the verified email addresses associated with the CC account.
+	 * See: https://developer.constantcontact.com/api_reference/index.html#!/Account_Services/retrieveEmailAddresses.
+	 */
+	public function get_verified_email_addresses() {
+		$cc              = $this->get_sdk();
+		$email_addresses = (array) $cc->get_email_addresses( [ 'confirm_status' => 'CONFIRMED' ] );
+
+		return array_map(
+			function( $email ) {
+				return $email->email_address;
+			},
+			$email_addresses
+		);
+	}
+
+	/**
+	 * Get a payload for syncing post data to the ESP campaign.
+	 *
+	 * @param WP_Post|int $post Post object or ID.
+	 * @return object Payload for syncing.
+	 */
+	public function get_sync_payload( $post ) {
+		$cc              = $this->get_sdk();
+		$renderer        = new Newspack_Newsletters_Renderer();
+		$content         = $renderer->retrieve_email_html( $post );
+		$auto_draft_html = '<html><body>[[trackingImage]]<p>Auto draft</p></body></html>';
+		$account_info    = $cc->get_account_info();
+		$sender_name     = get_post_meta( $post->ID, 'senderName', true );
+		$sender_email    = get_post_meta( $post->ID, 'senderEmail', true );
+
+		// If we don't have a sender name or email, set default values.
+		if ( ! $sender_name && $account_info->organization_name ) {
+			$sender_name = $account_info->organization_name;
+		} elseif ( ! $sender_name && $account_info->first_name && $account_info->last_name ) {
+			$sender_name = $account_info->first_name . ' ' . $account_info->last_name;
+		}
+
+		$verified_email_addresses = $this->get_verified_email_addresses();
+		if ( empty( $verified_email_addresses ) ) {
+			return new WP_Error(
+				'newspack_newsletters_constant_contact_error',
+				__( 'There are no verified email addresses in the Constant Contact account.', 'newspack-newsletters' )
+			);
+		}
+		if ( ! $sender_email ) {
+			$sender_email = $verified_email_addresses[0];
+		}
+		if ( ! in_array( $sender_email, $verified_email_addresses, true ) ) {
+			return new WP_Error(
+				'newspack_newsletters_constant_contact_error',
+				__( 'Sender email must be a verified Constant Contact account email address.', 'newspack-newsletters' )
+			);
+		}
+		$payload = [
+			'format_type'    => 5, // https://v3.developer.constantcontact.com/api_guide/email_campaigns_overview.html#collapse-format-types .
+			'html_content'   => empty( $content ) ? $auto_draft_html : $content,
+			'subject'        => $post->post_title,
+			'from_name'      => $sender_name ?? __( 'Sender Name', 'newspack-newsletters' ),
+			'from_email'     => $sender_email,
+			'reply_to_email' => $sender_email,
+		];
+		if ( $account_info->physical_address ) {
+			$payload['physical_address_in_footer'] = $account_info->physical_address;
+		}
+
+		// Sync send-to selections.
+		$send_lists = $this->get_send_lists( [ 'ids' => get_post_meta( $post->ID, 'send_list_id', true ) ] );
+		if ( ! empty( $send_lists[0] ) ) {
+			$send_list = $send_lists[0];
+			if ( 'list' === $send_list->get_entity_type() ) {
+				$payload['contact_list_ids'] = [ $send_list->get_id() ];
+			} elseif ( 'segment' === $send_list->get_entity_type() ) {
+				$payload['segment_ids'] = [ $send_list->get_id() ];
+			}
+		}
+
+		return $payload;
+	}
+
 	/**
 	 * Synchronize post with corresponding ESP campaign.
 	 *
@@ -598,21 +733,24 @@ public function sync( $post ) {
 				return;
 			}
 
-			$cc              = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc              = $this->get_sdk();
 			$cc_campaign_id  = get_post_meta( $post->ID, 'cc_campaign_id', true );
-			$renderer        = new Newspack_Newsletters_Renderer();
-			$content         = $renderer->retrieve_email_html( $post );
-			$auto_draft_html = '<html><body>[[trackingImage]]<p>Auto draft</p></body></html>';
-			$account_info    = $cc->get_account_info();
-
-			$activity_data = [
-				'format_type'  => 5, // https://v3.developer.constantcontact.com/api_guide/email_campaigns_overview.html#collapse-format-types .
-				'html_content' => empty( $content ) ? $auto_draft_html : $content,
-				'subject'      => $post->post_title,
-			];
-
-			if ( $account_info->physical_address ) {
-				$activity_data['physical_address_in_footer'] = $account_info->physical_address;
+			$payload         = $this->get_sync_payload( $post );
+
+			/**
+			 * Filter the metadata payload sent to CC when syncing.
+			 *
+			 * Allows custom tracking codes to be sent.
+			 *
+			 * @param array  $payload        CC payload.
+			 * @param object $post           Post object.
+			 * @param string $cc_campaign_id CC campaign ID, if defined.
+			 */
+			$payload = apply_filters( 'newspack_newsletters_cc_payload_sync', $payload, $post, $cc_campaign_id );
+
+			// If we have any errors in the payload, throw an exception.
+			if ( is_wp_error( $payload ) ) {
+				throw new Exception( esc_html( $payload->get_error_message() ) );
 			}
 
 			if ( $cc_campaign_id ) {
@@ -620,72 +758,31 @@ public function sync( $post ) {
 
 				// Constant Constact only allow updates on DRAFT or SENT status.
 				if ( ! in_array( $campaign->current_status, [ 'DRAFT', 'SENT' ], true ) ) {
-					return;
+					throw new Exception(
+						__( 'The newsletter campaign must have a DRAFT or SENT status.', 'newspack-newsletters' )
+					);
 				}
 
-				$activity = array_merge(
-					$activity_data,
-					[
-						'contact_list_ids' => $campaign->activity->contact_list_ids,
-						'from_name'        => $campaign->activity->from_name,
-						'from_email'       => $campaign->activity->from_email,
-						'reply_to_email'   => $campaign->activity->reply_to_email,
-					]
-				);
+				$cc->update_campaign_activity( $campaign->activity->campaign_activity_id, $payload );
 
-				$activity_result = $cc->update_campaign_activity( $campaign->activity->campaign_activity_id, $activity );
-				$name_result = $cc->update_campaign_name( $cc_campaign_id, $this->get_campaign_name( $post ) );
+				// Update campaign name.
+				$campaign_name = $this->get_campaign_name( $post );
+				if ( $campaign->name !== $campaign_name ) {
+					$cc->update_campaign_name( $cc_campaign_id, $campaign_name );
+				}
 
 				$campaign_result = $cc->get_campaign( $cc_campaign_id );
 			} else {
-
-				$initial_sender = __( 'Sender Name', 'newspack-newsletters' );
-				if ( $account_info->organization_name ) {
-					$initial_sender = $account_info->organization_name;
-				} elseif ( $account_info->first_name && $account_info->last_name ) {
-					$initial_sender = $account_info->first_name . ' ' . $account_info->last_name;
-				}
-
-				$email_addresses          = (array) $cc->get_email_addresses();
-				$verified_email_addresses = array_values(
-					array_filter(
-						$email_addresses,
-						function ( $email ) {
-							return 'CONFIRMED' === $email->confirm_status;
-						}
-					)
-				);
-
-				if ( empty( $verified_email_addresses ) ) {
-					throw new Exception( __( 'There are no verified email addresses in the Constant Contact account.', 'newspack-newsletters' ) );
-				}
-
-				$initial_email_address = $verified_email_addresses[0]->email_address;
-
 				$campaign = [
 					'name'                      => $this->get_campaign_name( $post ),
-					'email_campaign_activities' => [
-						array_merge(
-							$activity_data,
-							[
-								'subject'        => $post->post_title,
-								'from_name'      => $initial_sender,
-								'from_email'     => $initial_email_address,
-								'reply_to_email' => $initial_email_address,
-							]
-						),
-					],
+					'email_campaign_activities' => [ $payload ],
 				];
 
 				$campaign_result = $cc->create_campaign( $campaign );
 			}
 			update_post_meta( $post->ID, 'cc_campaign_id', $campaign_result->campaign_id );
 
-			// Retrieve and store campaign data.
-			$this->retrieve( $post->ID );
-
 			return $campaign_result;
-
 		} catch ( Exception $e ) {
 			set_transient( $transient_name, __( 'Error syncing with ESP. ', 'newspack-newsletters' ) . $e->getMessage(), 45 );
 			return new WP_Error( 'newspack_newsletters_constant_contact_error', $e->getMessage() );
@@ -748,7 +845,7 @@ public function send( $post ) {
 		}
 
 		try {
-			$cc = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc = $this->get_sdk();
 			$cc->create_schedule( $sync_result->activity->campaign_activity_id );
 		} catch ( Exception $e ) {
 			return new WP_Error(
@@ -784,7 +881,7 @@ public function trash( $post_id ) {
 				return;
 			}
 
-			$cc = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+			$cc = $this->get_sdk();
 
 			$campaign = $cc->get_campaign( $cc_campaign_id );
 			if ( $campaign && 'DRAFT' === $campaign->current_status ) {
@@ -821,23 +918,144 @@ public function get_lists() {
 			return $this->lists;
 		}
 		try {
-			$cc = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
-			$this->lists = array_map(
-				function ( $list ) {
-					return [
-						'id'               => $list->list_id,
-						'name'             => $list->name,
-						'membership_count' => $list->membership_count,
-					];
-				},
-				$cc->get_contact_lists()
-			);
+			$cc = $this->get_sdk();
+			if ( ! $this->lists ) {
+				$this->lists = array_map(
+					function ( $list ) {
+						return [
+							'id'               => $list->list_id,
+							'name'             => $list->name,
+							'membership_count' => $list->membership_count,
+						];
+					},
+					$cc->get_contact_lists()
+				);
+			}
+
 			return $this->lists;
 		} catch ( Exception $e ) {
 			return new WP_Error( 'newspack_newsletters_error', $e->getMessage() );
 		}
 	}
 
+	/**
+	 * Get segments.
+	 *
+	 * @return array|WP_Error List of existing segments or error.
+	 */
+	public function get_segments() {
+		if ( null !== $this->segments ) {
+			return $this->segments;
+		}
+		try {
+			$cc = $this->get_sdk();
+			if ( ! $this->segments ) {
+				$this->segments = array_map(
+					function ( $segment ) {
+						return [
+							'id'   => $segment->segment_id,
+							'name' => $segment->name,
+						];
+					},
+					$cc->get_segments()
+				);
+			}
+
+			return $this->segments;
+		} catch ( Exception $e ) {
+			return new WP_Error( 'newspack_newsletters_error', $e->getMessage() );
+		}
+	}
+
+	/**
+	 * Get all applicable lists and segments as Send_List objects.
+	 * Note that in CC, campaigns can be sent to either lists or segments, not both,
+	 * so both entity types should be treated as top-level send lists.
+	 *
+	 * @param array $args Array of search args. See Send_Lists::get_default_args() for supported params and default values.
+	 *
+	 * @return Send_List[]|WP_Error Array of Send_List objects on success, or WP_Error object on failure.
+	 */
+	public function get_send_lists( $args = [] ) {
+		$lists = $this->get_lists();
+		if ( is_wp_error( $lists ) ) {
+			return $lists;
+		}
+		$send_lists = array_map(
+			function( $list ) {
+				$config = [
+					'provider'    => $this->service,
+					'type'        => 'list',
+					'id'          => $list['id'],
+					'name'        => $list['name'],
+					'entity_type' => 'list',
+					'count'       => $list['membership_count'],
+					'edit_link'   => 'https://app.constantcontact.com/pages/contacts/ui#contacts/' . $list['id'],
+				];
+
+				return new Send_List( $config );
+			},
+			$lists
+		);
+		$segments = $this->get_segments();
+		if ( is_wp_error( $segments ) ) {
+			return $segments;
+		}
+		$send_segments = array_map(
+			function( $segment ) {
+				$segment_id = (string) $segment['id'];
+				$config      = [
+					'provider'    => $this->service,
+					'type'        => 'list', // In CC, segments and lists have the same hierarchy.
+					'id'          => $segment_id,
+					'name'        => $segment['name'],
+					'entity_type' => 'segment',
+					'edit_link'   => "https://app.constantcontact.com/pages/contacts/ui#segments/$segment_id/preview",
+				];
+
+				return new Send_List( $config );
+			},
+			$segments
+		);
+		$send_lists     = array_merge( $send_lists, $send_segments );
+		$filtered_lists = $send_lists;
+		if ( ! empty( $args['ids'] ) ) {
+			$ids           = ! is_array( $args['ids'] ) ? [ $args['ids'] ] : $args['ids'];
+			$filtered_lists = array_values(
+				array_filter(
+					$send_lists,
+					function ( $list ) use ( $ids ) {
+						return Send_Lists::matches_id( $ids, $list->get_id() );
+					}
+				)
+			);
+		}
+		if ( ! empty( $args['search'] ) ) {
+			$search        = ! is_array( $args['search'] ) ? [ $args['search'] ] : $args['search'];
+			$filtered_lists = array_values(
+				array_filter(
+					$send_lists,
+					function ( $list ) use ( $search ) {
+						return Send_Lists::matches_search(
+							$search,
+							[
+								$list->get_id(),
+								$list->get_name(),
+								$list->get_entity_type(),
+							]
+						);
+					}
+				)
+			);
+		}
+
+		if ( ! empty( $args['limit'] ) ) {
+			$filtered_lists = array_slice( $filtered_lists, 0, $args['limit'] );
+		}
+
+		return $filtered_lists;
+	}
+
 	/**
 	 * Add contact to a list or update an existing contact.
 	 *
@@ -853,7 +1071,7 @@ function ( $list ) {
 	 * @return array|WP_Error Contact data if the contact was added or error if failed.
 	 */
 	public function add_contact( $contact, $list_id = false ) {
-		$cc   = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc   = $this->get_sdk();
 		$data = [];
 		if ( $list_id ) {
 			$data['list_ids'] = [ $list_id ];
@@ -895,7 +1113,7 @@ public function add_contact( $contact, $list_id = false ) {
 	 * @return array|WP_Error Response or error if contact was not found.
 	 */
 	public function get_contact_data( $email, $return_details = false ) {
-		$cc      = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc      = $this->get_sdk();
 		$contact = $cc->get_contact( $email );
 		if ( ! $contact || is_wp_error( $contact ) ) {
 			return new WP_Error(
@@ -939,7 +1157,7 @@ public function get_contact_lists( $email ) {
 	 * @return true|WP_Error True if the contact was updated or error.
 	 */
 	public function update_contact_lists( $email, $lists_to_add = [], $lists_to_remove = [] ) {
-		$cc           = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc           = $this->get_sdk();
 		$contact_data = $this->get_contact_data( $email );
 		if ( is_wp_error( $contact_data ) ) {
 			/** Create contact */
@@ -986,6 +1204,10 @@ public static function get_labels( $context = '' ) {
 				'name'                   => 'Constant Contact',
 				'list_explanation'       => __( 'Constant Contact List', 'newspack-newsletters' ),
 				'local_list_explanation' => __( 'Constant Contact Tag', 'newspack-newsletters' ),
+				'list'                   => __( 'list or segment', 'newspack-newsletters' ), // "list" in lower case singular format.
+				'lists'                  => __( 'lists or segments', 'newspack-newsletters' ), // "list" in lower case plural format.
+				'List'                   => __( 'List or Segment', 'newspack-newsletters' ), // "list" in uppercase case singular format.
+				'Lists'                  => __( 'Lists or Segments', 'newspack-newsletters' ), // "list" in uppercase case plural format.
 			]
 		);
 	}
@@ -999,7 +1221,7 @@ public static function get_labels( $context = '' ) {
 	 * @return int|WP_Error The tag ID on success. WP_Error on failure.
 	 */
 	public function get_tag_id( $tag_name, $create_if_not_found = true, $list_id = null ) {
-		$cc  = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc  = $this->get_sdk();
 		$tag = $cc->get_tag_by_name( $tag_name );
 		if ( is_wp_error( $tag ) && $create_if_not_found ) {
 			$tag = $this->create_tag( $tag_name );
@@ -1018,7 +1240,7 @@ public function get_tag_id( $tag_name, $create_if_not_found = true, $list_id = n
 	 * @return string|WP_Error The tag name on success. WP_Error on failure.
 	 */
 	public function get_tag_by_id( $tag_id, $list_id = null ) {
-		$cc  = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc  = $this->get_sdk();
 		$tag = $cc->get_tag_by_id( $tag_id );
 		if ( is_wp_error( $tag ) ) {
 			return $tag;
@@ -1034,7 +1256,7 @@ public function get_tag_by_id( $tag_id, $list_id = null ) {
 	 * @return array|WP_Error The tag representation with at least 'id' and 'name' keys on succes. WP_Error on failure.
 	 */
 	public function create_tag( $tag, $list_id = null ) {
-		$cc  = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc  = $this->get_sdk();
 		$tag = $cc->create_tag( $tag );
 		if ( is_wp_error( $tag ) ) {
 			return $tag;
@@ -1056,7 +1278,7 @@ public function create_tag( $tag, $list_id = null ) {
 	 * @return array|WP_Error The tag representation with at least 'id' and 'name' keys on succes. WP_Error on failure.
 	 */
 	public function update_tag( $tag_id, $tag, $list_id = null ) {
-		$cc  = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc  = $this->get_sdk();
 		$tag = $cc->update_tag( $tag_id, $tag );
 		if ( is_wp_error( $tag ) ) {
 			return $tag;
@@ -1084,7 +1306,7 @@ public function add_tag_to_contact( $email, $tag, $list_id = null ) {
 			return true;
 		}
 		$new_tags = array_merge( $tags, [ $tag ] );
-		$cc       = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc       = $this->get_sdk();
 		return $cc->upsert_contact( $email, [ 'taggings' => $new_tags ] );
 	}
 
@@ -1102,7 +1324,7 @@ public function remove_tag_from_contact( $email, $tag, $list_id = null ) {
 		if ( count( $new_tags ) === count( $tags ) ) {
 			return true;
 		}
-		$cc = new Newspack_Newsletters_Constant_Contact_SDK( $this->api_key(), $this->api_secret(), $this->access_token() );
+		$cc = $this->get_sdk();
 		return $cc->upsert_contact( $email, [ 'taggings' => $new_tags ] );
 	}
 
diff --git a/includes/service-providers/interface-newspack-newsletters-esp-service.php b/includes/service-providers/interface-newspack-newsletters-esp-service.php
index bec6ad564..c0d1efc1d 100644
--- a/includes/service-providers/interface-newspack-newsletters-esp-service.php
+++ b/includes/service-providers/interface-newspack-newsletters-esp-service.php
@@ -50,17 +50,6 @@ public function list( $post_id, $list_id );
 	 */
 	public function retrieve( $post_id );
 
-	/**
-	 * Set sender data.
-	 *
-	 * @param string $post_id   Numeric ID of the campaign.
-	 * @param string $from_name Sender name.
-	 * @param string $reply_to  Reply to email address.
-	 *
-	 * @return array|WP_Error API Response or error.
-	 */
-	public function sender( $post_id, $from_name, $reply_to );
-
 	/**
 	 * Send test email or emails.
 	 *
@@ -87,6 +76,15 @@ public function sync( $post );
 	 */
 	public function get_lists();
 
+	/**
+	 * Get the ESP's available lists and sublists, reformatted as Send_List items.
+	 *
+	 * @param array $args Array of search args. See Send_Lists::get_default_args() for supported params and default values.
+	 *
+	 * @return array|WP_Error API Response or error.
+	 */
+	public function get_send_lists( $args );
+
 	/**
 	 * Add contact to a list.
 	 *
diff --git a/includes/service-providers/letterhead/class-newspack-newsletters-letterhead.php b/includes/service-providers/letterhead/class-newspack-newsletters-letterhead.php
index 3c2a7e25d..84904680d 100644
--- a/includes/service-providers/letterhead/class-newspack-newsletters-letterhead.php
+++ b/includes/service-providers/letterhead/class-newspack-newsletters-letterhead.php
@@ -70,6 +70,15 @@ public function get_lists() {
 		// TODO: Implement get_lists() method.
 	}
 
+	/**
+	 * Get send lists
+	 *
+	 * @param array $args Array of search args. See Send_Lists::get_default_args() for supported params and default values.
+	 *
+	 * @return object|void|null API Response or Error
+	 */
+	public function get_send_lists( $args = [] ) {} // Not used.
+
 	/**
 	 * This will call the Letterhead promotions API with the specific date passed as the
 	 * argument and the appropriate credentials. It will return an array.
diff --git a/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-cached-data.php b/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-cached-data.php
index 811c200d2..ef6b4d768 100644
--- a/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-cached-data.php
+++ b/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-cached-data.php
@@ -130,6 +130,35 @@ private static function get_mc_api() {
 		}
 	}
 
+	/**
+	 * Get audiences (lists).
+	 *
+	 * @param int|null $limit (Optional) The maximum number of items to return. If not given, will get all items.
+	 *
+	 * @throws Exception In case of errors while fetching data from the server.
+	 * @return array|WP_Error The audiences, or WP_Error if there was an error.
+	 */
+	public static function get_lists( $limit = null ) {
+		// If we've already gotten or fetched lists in this request, return those.
+		if ( ! empty( self::$memoized_data['lists'] ) ) {
+			return self::$memoized_data['lists'];
+		}
+
+		$data = get_option( self::get_lists_cache_key() );
+		if ( ! $data || self::is_cache_expired() ) {
+			Newspack_Newsletters_Logger::log( 'Mailchimp cache: No data found. Fetching lists from ESP.' );
+			$data = self::fetch_lists( $limit );
+		} else {
+			Newspack_Newsletters_Logger::log( 'Mailchimp cache: serving from cache' );
+		}
+
+		self::$memoized_data['lists'] = $data;
+		if ( $limit ) {
+			$data = array_slice( $data, 0, $limit );
+		}
+		return $data;
+	}
+
 	/**
 	 * Get segments of a given audience (list)
 	 *
@@ -200,6 +229,13 @@ private static function get_mc_instance() {
 		return Newspack_Newsletters_Mailchimp::instance();
 	}
 
+	/**
+	 * Get the cache key for the cached lists data.
+	 */
+	private static function get_lists_cache_key() {
+		return self::OPTION_PREFIX . '_lists';
+	}
+
 	/**
 	 * Get the cache key for a given list
 	 *
@@ -211,12 +247,12 @@ private static function get_cache_key( $list_id ) {
 	}
 
 	/**
-	 * Get the cache date key for a given list
+	 * Get the cache date key for a given list or all lists
 	 *
-	 * @param string $list_id The List ID.
+	 * @param string $list_id The List ID, or 'lists' for the cached lists data.
 	 * @return string The cache key
 	 */
-	private static function get_cache_date_key( $list_id ) {
+	private static function get_cache_date_key( $list_id = 'lists' ) {
 		return self::OPTION_PREFIX . '_date_' . $list_id;
 	}
 
@@ -226,7 +262,7 @@ private static function get_cache_date_key( $list_id ) {
 	 * @param string $list_id The List ID.
 	 * @return boolean
 	 */
-	private static function is_cache_expired( $list_id ) {
+	private static function is_cache_expired( $list_id = null ) {
 		$cache_date = get_option( self::get_cache_date_key( $list_id ) );
 		return $cache_date && ( time() - $cache_date ) > 20 * MINUTE_IN_SECONDS;
 	}
@@ -390,10 +426,15 @@ private static function get_data( $list_id ) {
 	/**
 	 * Dispatches a new request to refresh the cache
 	 *
-	 * @param string $list_id The List ID.
+	 * @param string $list_id The List ID or null for the cache for all lists.
 	 * @return void
 	 */
-	private static function dispatch_refresh( $list_id ) {
+	private static function dispatch_refresh( $list_id = null ) {
+		// If no list_id is provided, refresh the lists cache.
+		if ( ! $list_id ) {
+			self::fetch_lists();
+			return;
+		}
 
 		if ( ! function_exists( 'wp_create_nonce' ) ) {
 			require_once ABSPATH . WPINC . '/pluggable.php';
@@ -484,38 +525,89 @@ private static function refresh_cached_data( $list_id ) {
 	 */
 	public static function handle_cron() {
 		Newspack_Newsletters_Logger::log( 'Mailchimp cache: Handling cron request to refresh cache' );
+		$lists = self::get_lists();
+
+		foreach ( $lists as $list ) {
+			Newspack_Newsletters_Logger::log( 'Mailchimp cache: Dispatching request to refresh cache for list ' . $list['id'] );
+			self::dispatch_refresh( $list['id'] );
+		}
+	}
+
+	/**
+	 * Fetches all audiences (lists) from the Mailchimp server
+	 *
+	 * @param int|null $limit (Optional) The maximum number of items to return. If not given, will get all items.
+	 *
+	 * @throws Exception In case of errors while fetching data from the server.
+	 * @return array|WP_Error The audiences, or WP_Error if there was an error.
+	 */
+	public static function fetch_lists( $limit = null ) {
 		$mc = self::get_mc_api();
 		if ( \is_wp_error( $mc ) ) {
-			return;
+			return [];
 		}
 		$lists_response = ( self::get_mc_instance() )->validate(
 			$mc->get(
 				'lists',
 				[
-					'count'  => 1000,
-					'fields' => [ 'id' ],
+					'count'  => $limit ?? 1000,
+					'fields' => 'lists.name,lists.id,lists.web_id,lists.stats.member_count',
 				]
 			),
 			__( 'Error retrieving Mailchimp lists.', 'newspack_newsletters' )
 		);
 		if ( is_wp_error( $lists_response ) || empty( $lists_response['lists'] ) ) {
-			return;
+			Newspack_Newsletters_Logger::log( 'Mailchimp cache: Error refreshing cache: ' . ( $lists_response->getMessage() ?? __( 'Error retrieving Mailchimp lists.', 'newspack_newsletters' ) ) );
+			return is_wp_error( $lists_response ) ? $lists_response : [];
 		}
 
-		foreach ( $lists_response['lists'] as $list ) {
-			Newspack_Newsletters_Logger::log( 'Mailchimp cache: Dispatching request to refresh cache for list ' . $list['id'] );
-			self::dispatch_refresh( $list['id'] );
+		// Cache the lists (only if we got them all).
+		if ( ! $limit ) {
+			update_option( self::get_lists_cache_key(), $lists_response['lists'], false ); // auto-load false.
+			update_option( self::get_cache_date_key(), time(), false ); // auto-load false.
 		}
+
+		return $lists_response['lists'];
 	}
 
 	/**
-	 * Fetches the segments for a given List from the Mailchimp server
+	 * Fetches a single segment by segment ID + list ID.
 	 *
+	 * @param string $segment_id The segment ID.
 	 * @param string $list_id The audience (list) ID.
+	 *
+	 * @throws Exception In case of errors while fetching data from the server.
+	 * @return array The audience segment
+	 */
+	public static function fetch_segment( $segment_id, $list_id ) {
+		$mc = self::get_mc_api();
+		if ( \is_wp_error( $mc ) ) {
+			return $mc;
+		}
+		$response = ( self::get_mc_instance() )->validate(
+			$mc->get(
+				"lists/$list_id/segment/$segment_id",
+				[
+					'fields' => 'id,name,member_count,type,options,list_id',
+				],
+				60
+			),
+			__( 'Error retrieving Mailchimp segment with ID: ', 'newspack_newsletters' ) . $segment_id
+		);
+
+		return $response;
+	}
+
+	/**
+	 * Fetches the segments for a given List from the Mailchimp server
+	 *
+	 * @param string   $list_id The audience (list) ID.
+	 * @param int|null $limit (Optional) The maximum number of items to return. If not given, will get all items.
+	 *
 	 * @throws Exception In case of errors while fetching data from the server.
 	 * @return array The audience segments
 	 */
-	public static function fetch_segments( $list_id ) {
+	public static function fetch_segments( $list_id, $limit = null ) {
 		$segments = [];
 
 		$mc = self::get_mc_api();
@@ -528,7 +620,7 @@ public static function fetch_segments( $list_id ) {
 				"lists/$list_id/segments",
 				[
 					'type'  => 'saved', // 'saved' or 'static' segments. 'static' segments are actually the same thing as tags, so we can exclude them from this request as we fetch tags separately.
-					'count' => 1000,
+					'count' => $limit ?? 1000,
 				],
 				60
 			),
@@ -542,17 +634,19 @@ public static function fetch_segments( $list_id ) {
 	/**
 	 * Fetches the interest_categories (aka Groups) for a given List from the Mailchimp server
 	 *
-	 * @param string $list_id The audience (list) ID.
+	 * @param string   $list_id The audience (list) ID.
+	 * @param int|null $limit (Optional) The maximum number of items to return. If not given, will get all items.
+	 *
 	 * @throws Exception In case of errors while fetching data from the server.
 	 * @return array The audience interest_categories
 	 */
-	private static function fetch_interest_categories( $list_id ) {
+	private static function fetch_interest_categories( $list_id, $limit = null ) {
 		$mc = self::get_mc_api();
 		if ( \is_wp_error( $mc ) ) {
 			return [];
 		}
 		$interest_categories = $list_id ? ( self::get_mc_instance() )->validate(
-			$mc->get( "lists/$list_id/interest-categories", [ 'count' => 1000 ], 60 ),
+			$mc->get( "lists/$list_id/interest-categories", [ 'count' => $limit ?? 1000 ], 60 ),
 			__( 'Error retrieving Mailchimp groups.', 'newspack_newsletters' )
 		) : null;
 
@@ -560,7 +654,7 @@ private static function fetch_interest_categories( $list_id ) {
 			foreach ( $interest_categories['categories'] as &$category ) {
 				$category_id           = $category['id'];
 				$category['interests'] = ( self::get_mc_instance() )->validate(
-					$mc->get( "lists/$list_id/interest-categories/$category_id/interests", [ 'count' => 1000 ], 60 ),
+					$mc->get( "lists/$list_id/interest-categories/$category_id/interests", [ 'count' => $limit ?? 1000 ], 60 ),
 					__( 'Error retrieving Mailchimp groups.', 'newspack_newsletters' )
 				);
 			}
@@ -572,11 +666,13 @@ private static function fetch_interest_categories( $list_id ) {
 	/**
 	 * Fetches the tags for a given audience (list) from the Mailchimp server
 	 *
-	 * @param string $list_id The audience (list) ID.
+	 * @param string   $list_id The audience (list) ID.
+	 * @param int|null $limit (Optional) The maximum number of items to return. If not given, will get all items.
+	 *
 	 * @throws Exception In case of errors while fetching data from the server.
 	 * @return array The audience tags
 	 */
-	public static function fetch_tags( $list_id ) {
+	public static function fetch_tags( $list_id, $limit = null ) {
 		$mc = self::get_mc_api();
 		if ( \is_wp_error( $mc ) ) {
 			return [];
@@ -586,7 +682,7 @@ public static function fetch_tags( $list_id ) {
 				"lists/$list_id/segments",
 				[
 					'type'  => 'static', // 'saved' or 'static' segments. Tags are called 'static' segments in Mailchimp's API.
-					'count' => 1000,
+					'count' => $limit ?? 1000,
 				],
 				60
 			),
diff --git a/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-controller.php b/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-controller.php
index 48deb7c7a..44ebbd7c0 100644
--- a/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-controller.php
+++ b/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp-controller.php
@@ -42,14 +42,10 @@ public static function register_meta() {
 		);
 		\register_meta(
 			'post',
-			'mc_list_id',
+			'mc_folder_id',
 			[
 				'object_subtype' => Newspack_Newsletters::NEWSPACK_NEWSLETTERS_CPT,
-				'show_in_rest'   => [
-					'schema' => [
-						'context' => [ 'edit' ],
-					],
-				],
+				'show_in_rest'   => true,
 				'type'           => 'string',
 				'single'         => true,
 				'auth_callback'  => '__return_true',
@@ -67,11 +63,11 @@ public function register_routes() {
 
 		\register_rest_route(
 			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)',
+			'(?P<id>[\a-z]+)/retrieve',
 			[
 				'methods'             => \WP_REST_Server::READABLE,
 				'callback'            => [ $this, 'api_retrieve' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id' => [
 						'sanitize_callback' => 'absint',
@@ -86,7 +82,7 @@ public function register_routes() {
 			[
 				'methods'             => \WP_REST_Server::EDITABLE,
 				'callback'            => [ $this, 'api_test' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
+				'permission_callback' => [ 'Newspack_Newsletters', 'api_authoring_permissions_check' ],
 				'args'                => [
 					'id'         => [
 						'sanitize_callback' => 'absint',
@@ -98,84 +94,6 @@ public function register_routes() {
 				],
 			]
 		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/sender',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_sender' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'        => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'from_name' => [
-						'sanitize_callback' => 'sanitize_text_field',
-					],
-					'reply_to'  => [
-						'sanitize_callback' => 'sanitize_email',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/folder',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_folder' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'        => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'list_id'   => [
-						'sanitize_callback' => 'esc_attr',
-					],
-					'folder_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/list/(?P<list_id>[\a-z]+)',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_list' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'      => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'list_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
-		\register_rest_route(
-			$this->service_provider::BASE_NAMESPACE . $this->service_provider->service,
-			'(?P<id>[\a-z]+)/segments',
-			[
-				'methods'             => \WP_REST_Server::EDITABLE,
-				'callback'            => [ $this, 'api_segments' ],
-				'permission_callback' => [ $this->service_provider, 'api_authoring_permissions_check' ],
-				'args'                => [
-					'id'        => [
-						'sanitize_callback' => 'absint',
-						'validate_callback' => [ 'Newspack_Newsletters', 'validate_newsletter_id' ],
-					],
-					'target_id' => [
-						'sanitize_callback' => 'esc_attr',
-					],
-				],
-			]
-		);
 	}
 
 	/**
@@ -207,61 +125,4 @@ public function api_test( $request ) {
 		);
 		return self::get_api_response( $response );
 	}
-
-	/**
-	 * Set the sender name and email for the campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_sender( $request ) {
-		$response = $this->service_provider->sender(
-			$request['id'],
-			$request['from_name'],
-			$request['reply_to']
-		);
-		return self::get_api_response( $response );
-	}
-
-	/**
-	 * Set folder for a campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_folder( $request ) {
-		$response = $this->service_provider->folder(
-			$request['id'],
-			$request['folder_id']
-		);
-		return self::get_api_response( $response );
-	}
-
-	/**
-	 * Set list for a campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_list( $request ) {
-		$response = $this->service_provider->list(
-			$request['id'],
-			$request['list_id']
-		);
-		return self::get_api_response( $response );
-	}
-
-	/**
-	 * Set Mailchimp audience segments for a campaign.
-	 *
-	 * @param WP_REST_Request $request API request object.
-	 * @return WP_REST_Response|mixed API response or error.
-	 */
-	public function api_segments( $request ) {
-		$response = $this->service_provider->audience_segments(
-			$request['id'],
-			$request['target_id']
-		);
-		return self::get_api_response( $response );
-	}
 }
diff --git a/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp.php b/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp.php
index 21a64df6e..8c4dd067f 100644
--- a/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp.php
+++ b/includes/service-providers/mailchimp/class-newspack-newsletters-mailchimp.php
@@ -10,6 +10,8 @@
 use DrewM\MailChimp\MailChimp;
 use Newspack\Newsletters\Subscription_List;
 use Newspack\Newsletters\Subscription_Lists;
+use Newspack\Newsletters\Send_Lists;
+use Newspack\Newsletters\Send_List;
 
 /**
  * Main Newspack Newsletters Class.
@@ -19,18 +21,18 @@ final class Newspack_Newsletters_Mailchimp extends \Newspack_Newsletters_Service
 	use Newspack_Newsletters_Mailchimp_Groups;
 
 	/**
-	 * Whether the provider has support to tags and tags based Subscription Lists.
+	 * Provider name.
 	 *
-	 * @var boolean
+	 * @var string
 	 */
-	public static $support_local_lists = true;
+	public $name = 'Mailchimp';
 
 	/**
-	 * Provider name.
+	 * Whether the provider has support to tags and tags based Subscription Lists.
 	 *
-	 * @var string
+	 * @var boolean
 	 */
-	public $name = 'Mailchimp';
+	public static $support_local_lists = true;
 
 	/**
 	 * Cache of contact added on execution. Control to avoid adding the same
@@ -111,6 +113,20 @@ public function api_key() {
 		return $credentials['api_key'];
 	}
 
+	/**
+	 * Get the base URL for the Mailchimp admin dashboard.
+	 *
+	 * @return string|boolean The URL on success. False on failure.
+	 */
+	public function get_admin_url() {
+		$api_key = $this->api_key();
+		if ( strpos( $api_key, '-' ) === false ) {
+			return false;
+		}
+		list(, $data_center) = explode( '-', $api_key );
+		return 'https://' . $data_center . '.admin.mailchimp.com/';
+	}
+
 	/**
 	 * Set the API credentials for the service provider.
 	 *
@@ -315,6 +331,15 @@ public function remove_tag_from_contact( $email, $tag, $list_id = null ) {
 		);
 	}
 
+	/**
+	 * Get available campaign folders.
+	 *
+	 * @return array|WP_Error List of folders or error.
+	 */
+	public function get_folders() {
+		return Newspack_Newsletters_Mailchimp_Cached_Data::get_folders();
+	}
+
 	/**
 	 * Set folder for a campaign.
 	 *
@@ -322,7 +347,7 @@ public function remove_tag_from_contact( $email, $tag, $list_id = null ) {
 	 * @param string $folder_id ID of the folder.
 	 * @return object|WP_Error API API Response or error.
 	 */
-	public function folder( $post_id, $folder_id ) {
+	public function folder( $post_id, $folder_id = '' ) {
 		$mc_campaign_id = get_post_meta( $post_id, 'mc_campaign_id', true );
 		if ( ! $mc_campaign_id ) {
 			return new WP_Error(
@@ -411,34 +436,94 @@ public function retrieve( $post_id ) {
 		}
 		try {
 			$mc_campaign_id = get_post_meta( $post_id, 'mc_campaign_id', true );
-			if ( ! $mc_campaign_id ) {
-				$this->sync( get_post( $post_id ) );
-			}
-			$mc                  = new Mailchimp( $this->api_key() );
-			$campaign            = $this->validate(
-				$mc->get( "campaigns/$mc_campaign_id" ),
-				__( 'Error retrieving Mailchimp campaign.', 'newspack_newsletters' )
-			);
-			$list_id = $campaign && isset( $campaign['recipients']['list_id'] ) ? $campaign['recipients']['list_id'] : null;
 
-			$lists = $this->get_lists( true );
-			if ( \is_wp_error( $lists ) ) {
-				return $lists;
+			// If there's no synced campaign ID yet, create it.
+			if ( ! $mc_campaign_id ) {
+				Newspack_Newsletters_Logger::log( 'Creating new campaign for post ID ' . $post_id );
+				$sync_result = $this->sync( get_post( $post_id ) );
+				if ( is_wp_error( $sync_result ) ) {
+					return $sync_result;
+				}
+				$campaign       = $sync_result['campaign_result'];
+				$mc_campaign_id = $campaign['id'];
+			} else {
+				Newspack_Newsletters_Logger::log( 'Retrieving campaign ' . $mc_campaign_id . ' for post ID ' . $post_id );
+				$mc                  = new Mailchimp( $this->api_key() );
+				$campaign            = $this->validate(
+					$mc->get(
+						"campaigns/$mc_campaign_id",
+						[
+							'fields' => 'id,type,status,emails_sent,content_type,recipients,settings',
+						]
+					),
+					__( 'Error retrieving Mailchimp campaign.', 'newspack_newsletters' )
+				);
 			}
 
+			$list_id         = $campaign['recipients']['list_id'] ?? null;
+			$send_list_id    = get_post_meta( $post_id, 'send_list_id', true );
+			$send_sublist_id = get_post_meta( $post_id, 'send_sublist_id', true );
 			$newsletter_data = [
-				'campaign'            => $campaign,
-				'campaign_id'         => $mc_campaign_id,
-				'folders'             => Newspack_Newsletters_Mailchimp_Cached_Data::get_folders(),
-				'interest_categories' => $this->get_interest_categories( $list_id ),
-				'lists'               => $lists,
-				'merge_fields'        => $list_id ? Newspack_Newsletters_Mailchimp_Cached_Data::get_merge_fields( $list_id ) : [],
-				'segments'            => $list_id ? Newspack_Newsletters_Mailchimp_Cached_Data::get_segments( $list_id ) : [],
-				'tags'                => $this->get_tags( $list_id ),
+				'campaign'               => $campaign,
+				'campaign_id'            => $mc_campaign_id,
+				'folders'                => Newspack_Newsletters_Mailchimp_Cached_Data::get_folders(),
+				'allowed_sender_domains' => $this->get_verified_domains(),
+				'merge_fields'           => $list_id ? Newspack_Newsletters_Mailchimp_Cached_Data::get_merge_fields( $list_id ) : [],
 			];
 
+			// Reconcile campaign settings with info fetched from the ESP for a true two-way sync.
+			if ( ! empty( $campaign['settings']['from_name'] ) && $campaign['settings']['from_name'] !== get_post_meta( $post_id, 'senderName', true ) ) {
+				$newsletter_data['senderName'] = $campaign['settings']['from_name']; // If campaign has different sender info set, update ours.
+			}
+			if ( ! empty( $campaign['settings']['reply_to'] ) && $campaign['settings']['reply_to'] !== get_post_meta( $post_id, 'senderEmail', true ) ) {
+				$newsletter_data['senderEmail'] = $campaign['settings']['reply_to']; // If campaign has different sender info set, update ours.
+			}
+			if ( $list_id && $list_id !== $send_list_id ) {
+				$newsletter_data['list_id'] = $list_id; // If campaign has a different list selected, update ours.
+				$send_list_id               = $list_id;
+
+				if ( ! empty( $campaign['recipients']['segment_opts'] ) ) {
+					$segment_opts  = $campaign['recipients']['segment_opts'];
+					$target_id_raw = $segment_opts['saved_segment_id'] ?? null;
+					if ( ! $target_id_raw ) {
+						$target_id_raw = $segment_opts['conditions'][0]['value'] ?? null;
+					}
+					if ( $target_id_raw ) {
+						$target_id = strval( is_array( $target_id_raw ) && ! empty( $target_id_raw[0] ) ? $target_id_raw[0] : $target_id_raw );
+						if ( ! $target_id ) {
+							$target_id = (string) $target_id_raw;
+						}
+						if ( $target_id && $target_id !== $send_sublist_id ) {
+							$newsletter_data['sublist_id'] = $target_id; // If campaign has a different sublist selected, update ours.
+							$send_sublist_id               = $target_id;
+						}
+					}
+				}
+			}
+
+			// Prefetch send list info if we have a selected list and/or sublist.
+			$newsletter_data['lists'] = $this->get_send_lists(
+				[
+					'ids'  => $send_list_id ? [ $send_list_id ] : null, // If we have a selected list, make sure to fetch it.
+					'type' => 'list',
+				]
+			);
+			$newsletter_data['sublists'] = $send_list_id || $send_sublist_id ? // Prefetch send lists only if we have something selected already.
+				$this->get_send_lists(
+					[
+						'ids'       => [ $send_sublist_id ], // If we have a selected sublist, make sure to fetch it. Otherwise, we'll populate sublists later.
+						'parent_id' => $send_list_id,
+						'type'      => 'sublist',
+					]
+				) :
+				[];
+
 			return $newsletter_data;
 		} catch ( Exception $e ) {
+			// If we couldn't get the campaign, delete the mc_campaign_id so it gets recreated on the next sync.
+			delete_post_meta( $post_id, 'mc_campaign_id' );
+			$this->retrieve( $post_id );
+
 			return new WP_Error(
 				'newspack_newsletters_mailchimp_error',
 				$e->getMessage()
@@ -455,92 +540,171 @@ public function retrieve( $post_id ) {
 	 * @return array|WP_Error List of subscription lists or error.
 	 */
 	public function get_lists( $audiences_only = false ) {
-		try {
-			$mc             = new Mailchimp( $this->api_key() );
-			$lists_response = $this->validate(
-				$mc->get(
-					'lists',
-					[
-						'count' => 1000,
-					]
-				),
-				__( 'Error retrieving Mailchimp lists.', 'newspack_newsletters' )
-			);
-			if ( is_wp_error( $lists_response ) ) {
-				return new WP_Error(
-					'newspack_newsletters_mailchimp_error',
-					$lists_response->getMessage()
-				);
-			}
+		$lists = Newspack_Newsletters_Mailchimp_Cached_Data::get_lists();
+		if ( $audiences_only || is_wp_error( $lists ) ) {
+			return $lists;
+		}
 
-			if ( ! isset( $lists_response['lists'] ) ) {
-				$error_message  = __( 'Error retrieving Mailchimp lists.', 'newspack_newsletters' );
-				$error_message .= ! empty( $lists_response['title'] ) ? ' ' . $lists_response['title'] : '';
-				return new WP_Error(
-					'newspack_newsletters_mailchimp_error',
-					$error_message
+		// In addition to Audiences, we also automatically fetch all groups and tags and offer them as Subscription Lists.
+		// Build the final list inside the loop so groups are added after the list they belong to and we can then represent the hierarchy in the UI.
+		foreach ( $lists as $list ) {
+
+			$lists[]        = $list;
+			$all_categories = Newspack_Newsletters_Mailchimp_Cached_Data::get_interest_categories( $list['id'] );
+			$all_categories = $all_categories['categories'] ?? [];
+			$all_tags       = Newspack_Newsletters_Mailchimp_Cached_Data::get_tags( $list['id'] ) ?? [];
+
+			foreach ( $all_categories as $found_category ) {
+
+				// Do not include groups under the category we use to store "Local" lists.
+				if ( $this->get_group_category_name() === $found_category['title'] ) {
+					continue;
+				}
+
+				$all_groups = $found_category['interests'] ?? [];
+
+				$groups = array_map(
+					function ( $group ) use ( $list ) {
+						$group['id']   = Subscription_List::mailchimp_generate_public_id( $group['id'], $list['id'] );
+						$group['type'] = 'mailchimp-group';
+						return $group;
+					},
+					$all_groups['interests'] ?? [] // Yes, two levels of 'interests'.
 				);
+				$lists  = array_merge( $lists, $groups );
 			}
 
-			if ( $audiences_only ) {
-				return $lists_response['lists'];
+			foreach ( $all_tags as $tag ) {
+				$tag['id']   = Subscription_List::mailchimp_generate_public_id( $tag['id'], $list['id'], 'tag' );
+				$tag['type'] = 'mailchimp-tag';
+				$lists[]     = $tag;
 			}
+		}
 
-			$lists = [];
+		// Reconcile edited names for locally-configured lists.
+		$configured_lists = Newspack_Newsletters_Subscription::get_lists_config();
+		if ( ! empty( $configured_lists ) ) {
+			foreach ( $lists as &$list ) {
+				if ( ! empty( $configured_lists[ $list['id'] ]['name'] ) ) {
+					$list['local_name'] = $configured_lists[ $list['id'] ]['name'];
+				}
+			}
+		}
 
-			// In addition to Audiences, we also automatically fetch all groups and tags and offer them as Subscription Lists.
-			// Build the final list inside the loop so groups are added after the list they belong to and we can then represent the hierarchy in the UI.
-			foreach ( $lists_response['lists'] as $list ) {
+		return $lists;
+	}
 
-				$lists[]        = $list;
-				$all_categories = Newspack_Newsletters_Mailchimp_Cached_Data::get_interest_categories( $list['id'] );
-				$all_categories = $all_categories['categories'] ?? [];
-				$all_tags       = Newspack_Newsletters_Mailchimp_Cached_Data::get_tags( $list['id'] ) ?? [];
+	/**
+	 * Get all applicable audiences, groups, tags, and segments as Send_List objects.
+	 *
+	 * @param array $args Array of search args. See Send_Lists::get_default_args() for supported params and default values.
+	 *
+	 * @return Send_List[]|WP_Error Array of Send_List objects on success, or WP_Error object on failure.
+	 */
+	public function get_send_lists( $args = [] ) {
+		$defaults   = Send_Lists::get_default_args();
+		$args       = wp_parse_args( $args, $defaults );
+		$by_id      = ! empty( $args['ids'] );
+		$admin_url  = self::get_admin_url();
+		$audiences  = Newspack_Newsletters_Mailchimp_Cached_Data::get_lists( $args['limit'] );
+		$send_lists = [];
+
+		$entity_type = 'audience';
+		foreach ( $audiences as $audience ) {
+			if ( ! empty( $args['parent_id'] ) && $audience['id'] !== $args['parent_id'] ) {
+				continue;
+			}
+			$matches = $by_id ? Send_Lists::matches_id( $args['ids'], $audience['id'] ) : Send_Lists::matches_search( $args['search'], [ $audience['id'], $audience['name'], $entity_type ] );
+			if ( ( ! $args['type'] || 'list' === $args['type'] ) && $matches ) {
+				$config = [
+					'provider'    => $this->service,
+					'type'        => 'list',
+					'id'          => $audience['id'],
+					'name'        => $audience['name'],
+					'entity_type' => $entity_type,
+					'count'       => $audience['stats']['member_count'] ?? 0,
+				];
+				if ( $admin_url && ! empty( $audience['web_id'] ) ) {
+					$config['edit_link'] = $admin_url . 'audience/contacts/?id=' . $audience['web_id'];
+				}
+				$send_lists[] = new Send_List( $config );
+			}
 
-				foreach ( $all_categories as $found_category ) {
+			if ( 'list' === $args['type'] ) {
+				continue;
+			}
 
-					// Do not include groups under the category we use to store "Local" lists.
-					if ( $this->get_group_category_name() === $found_category['title'] ) {
-						continue;
+			$groups      = Newspack_Newsletters_Mailchimp_Cached_Data::get_interest_categories( $audience['id'], $args['limit'] );
+			$entity_type = 'group';
+			if ( isset( $groups['categories'] ) ) {
+				foreach ( $groups['categories'] as $category ) {
+					if ( isset( $category['interests']['interests'] ) ) {
+						foreach ( $category['interests']['interests'] as $interest ) {
+							$matches = $by_id ? Send_Lists::matches_id( $args['ids'], $interest['id'] ) : Send_Lists::matches_search( $args['search'], [ $interest['id'], $interest['name'], $entity_type ] );
+							if ( $matches ) {
+								$config = [
+									'provider'    => $this->service,
+									'type'        => 'sublist',
+									'id'          => $interest['id'],
+									'name'        => $interest['name'],
+									'entity_type' => $entity_type,
+									'parent'      => $interest['list_id'],
+									'count'       => $interest['subscriber_count'],
+								];
+								if ( $admin_url && $audience['web_id'] ) {
+									$config['edit_link'] = $admin_url . 'audience/groups/?id=' . $audience['web_id'];
+								}
+								$send_lists[] = new Send_List( $config );
+							}
+						}
 					}
-
-					$all_groups = $found_category['interests'] ?? [];
-
-					$groups = array_map(
-						function ( $group ) use ( $list ) {
-							$group['id']   = Subscription_List::mailchimp_generate_public_id( $group['id'], $list['id'] );
-							$group['type'] = 'mailchimp-group';
-							return $group;
-						},
-						$all_groups['interests'] ?? [] // Yes, two levels of 'interests'.
-					);
-					$lists  = array_merge( $lists, $groups );
 				}
+			}
 
-				foreach ( $all_tags as $tag ) {
-					$tag['id']   = Subscription_List::mailchimp_generate_public_id( $tag['id'], $list['id'], 'tag' );
-					$tag['type'] = 'mailchimp-tag';
-					$lists[]     = $tag;
+			$tags        = Newspack_Newsletters_Mailchimp_Cached_Data::get_tags( $audience['id'], $args['limit'] );
+			$entity_type = 'tag';
+			foreach ( $tags as $tag ) {
+				$matches = $by_id ? Send_Lists::matches_id( $args['ids'], $tag['id'] ) : Send_Lists::matches_search( $args['search'], [ $tag['id'], $tag['name'], $entity_type ] );
+				if ( $matches ) {
+					$config = [
+						'provider'    => $this->service,
+						'type'        => 'sublist',
+						'id'          => $tag['id'],
+						'name'        => $tag['name'],
+						'entity_type' => $entity_type,
+						'parent'      => $tag['list_id'],
+						'count'       => $tag['member_count'],
+					];
+					if ( $admin_url && $audience['web_id'] ) {
+						$config['edit_link'] = $admin_url . 'audience/tags/?id=' . $audience['web_id'];
+					}
+					$send_lists[] = new Send_List( $config );
 				}
 			}
 
-			// Reconcile edited names for locally-configured lists.
-			$configured_lists = Newspack_Newsletters_Subscription::get_lists_config();
-			if ( ! empty( $configured_lists ) ) {
-				foreach ( $lists as &$list ) {
-					if ( ! empty( $configured_lists[ $list['id'] ]['name'] ) ) {
-						$list['local_name'] = $configured_lists[ $list['id'] ]['name'];
+			$segments    = Newspack_Newsletters_Mailchimp_Cached_Data::get_segments( ( $parent_id ?? $audience['id'] ), $args['limit'] );
+			$entity_type = 'segment';
+			foreach ( $segments as $segment ) {
+				$matches = $by_id ? Send_Lists::matches_id( $args['ids'], $segment['id'] ) : Send_Lists::matches_search( $args['search'], [ $segment['id'], $segment['name'], $entity_type ] );
+				if ( $matches ) {
+					$config = [
+						'provider'    => $this->service,
+						'type'        => 'sublist',
+						'id'          => $segment['id'],
+						'name'        => $segment['name'],
+						'entity_type' => $entity_type,
+						'parent'      => $segment['list_id'],
+						'count'       => $segment['member_count'],
+					];
+					if ( $admin_url && $audience['web_id'] ) {
+						$config['edit_link'] = $admin_url . 'audience/segments/?id=' . $audience['web_id'];
 					}
+					$send_lists[] = new Send_List( $config );
 				}
 			}
-
-			return $lists;
-		} catch ( Exception $e ) {
-			return new WP_Error(
-				'newspack_newsletters_mailchimp_error',
-				$e->getMessage()
-			);
 		}
+
+		return $send_lists;
 	}
 
 	/**
@@ -631,30 +795,19 @@ public function get_list_merge_fields( $list_id ) {
 	}
 
 	/**
-	 * Set sender data.
+	 * Get verified domains from the MC account.
 	 *
-	 * @param string $post_id Numeric ID of the campaign.
-	 * @param string $from_name Sender name.
-	 * @param string $reply_to Reply to email address.
-	 * @return object|WP_Error API Response or error.
+	 * @return array List of verified domains.
 	 */
-	public function sender( $post_id, $from_name, $reply_to ) {
-		$mc_campaign_id = get_post_meta( $post_id, 'mc_campaign_id', true );
-		if ( ! $mc_campaign_id ) {
-			return new WP_Error(
-				'newspack_newsletters_no_campaign_id',
-				__( 'Mailchimp campaign ID not found.', 'newspack-newsletters' )
-			);
-		}
-		try {
-			$mc = new Mailchimp( $this->api_key() );
-
-			$result = $this->validate(
-				$mc->get( 'verified-domains', [ 'count' => 1000 ] ),
-				__( 'Error retrieving verified domains from Mailchimp.', 'newspack-newsletters' )
-			);
+	public function get_verified_domains() {
+		$mc = new Mailchimp( $this->api_key() );
+		$result = $this->validate(
+			$mc->get( 'verified-domains', [ 'count' => 1000 ] ),
+			__( 'Error retrieving verified domains from Mailchimp.', 'newspack-newsletters' )
+		);
 
-			$verified_domains = array_filter(
+		return array_values(
+			array_filter(
 				array_map(
 					function ( $domain ) {
 						return $domain['verified'] ? strtolower( trim( $domain['domain'] ) ) : null;
@@ -664,10 +817,21 @@ function ( $domain ) {
 				function ( $domain ) {
 					return ! empty( $domain );
 				}
-			);
+			)
+		);
+	}
 
-			$explode = explode( '@', $reply_to );
-			$domain  = strtolower( trim( array_pop( $explode ) ) );
+	/**
+	 * Set sender data.
+	 *
+	 * @param string $email Reply to email address.
+	 * @return boolean|WP_Error True if the email address is valid, otherwise error.
+	 */
+	public function validate_sender_email( $email ) {
+		try {
+			$verified_domains = $this->get_verified_domains();
+			$explode         = explode( '@', $email );
+			$domain          = strtolower( trim( array_pop( $explode ) ) );
 
 			if ( ! in_array( $domain, $verified_domains ) ) {
 				return new WP_Error(
@@ -681,25 +845,7 @@ function ( $domain ) {
 				);
 			}
 
-			$settings = [];
-			if ( $from_name ) {
-				$settings['from_name'] = $from_name;
-			}
-			if ( $reply_to ) {
-				$settings['reply_to'] = $reply_to;
-			}
-			$payload = [
-				'settings' => $settings,
-			];
-			$result  = $this->validate(
-				$mc->patch( "campaigns/$mc_campaign_id", $payload ),
-				__( 'Error setting sender name and email.', 'newspack_newsletters' )
-			);
-
-			$data           = $this->retrieve( $post_id );
-			$data['result'] = $result;
-
-			return \rest_ensure_response( $data );
+			return true;
 		} catch ( Exception $e ) {
 			return new WP_Error(
 				'newspack_newsletters_mailchimp_error',
@@ -767,6 +913,110 @@ public function test( $post_id, $emails ) {
 		}
 	}
 
+	/**
+	 * Get a payload for syncing post data to the ESP campaign.
+	 *
+	 * @param WP_Post|int $post Post object or ID.
+	 * @return object Payload for syncing.
+	 */
+	public function get_sync_payload( $post ) {
+		if ( is_int( $post ) ) {
+			$post = get_post( $post );
+		}
+		$payload = [
+			'type'         => 'regular',
+			'content_type' => 'template',
+			'settings'     => [
+				'subject_line' => $post->post_title,
+				'title'        => $this->get_campaign_name( $post ),
+			],
+		];
+
+		// Sync sender name + email.
+		$sender_name  = get_post_meta( $post->ID, 'senderName', true );
+		$sender_email = get_post_meta( $post->ID, 'senderEmail', true );
+		if ( ! empty( $sender_name ) ) {
+			$payload['settings']['from_name'] = $sender_name;
+		}
+		if ( ! empty( $sender_email ) ) {
+			$is_valid_email = $this->validate_sender_email( $sender_email );
+			if ( is_wp_error( $is_valid_email ) ) {
+				delete_post_meta( $post->ID, 'senderEmail' ); // Delete invalid email so we can't accidentally attempt to send with it.
+				return $is_valid_email;
+			}
+			$payload['settings']['reply_to'] = $sender_email;
+		}
+
+		// Sync send-to selections.
+		$send_list_id = get_post_meta( $post->ID, 'send_list_id', true );
+		if ( ! empty( $send_list_id ) ) {
+			$payload['recipients'] = [
+				'list_id' => $send_list_id,
+			];
+			$send_sublist_id = get_post_meta( $post->ID, 'send_sublist_id', true );
+			if ( ! empty( $send_sublist_id ) ) {
+				$sublist = $this->get_send_lists(
+					[
+						'ids'       => [ $send_sublist_id ],
+						'limit'     => 1,
+						'parent_id' => $send_list_id,
+						'type'      => 'sublist',
+					]
+				);
+				if ( ! empty( $sublist[0]->get_entity_type() ) ) {
+					$sublist_type = $sublist[0]->get_entity_type();
+					switch ( $sublist_type ) {
+						case 'group':
+							$payload['recipients']['segment_opts'] = [
+								'match'      => 'all',
+								'conditions' => [
+									[
+										'condition_type' => 'Interests',
+										'field'          => 'interests-' . $send_sublist_id,
+										'op'             => 'interestcontains',
+										'value'          => [ $send_sublist_id ],
+									],
+								],
+							];
+							break;
+						case 'tag':
+							$payload['recipients']['segment_opts'] = [
+								'match'      => 'all',
+								'conditions' => [
+									[
+										'condition_type' => 'StaticSegment',
+										'field'          => 'static_segment',
+										'op'             => 'static_is',
+										'value'          => $send_sublist_id,
+									],
+								],
+							];
+							break;
+						case 'segment':
+							$segment_data = Newspack_Newsletters_Mailchimp_Cached_Data::fetch_segment( $send_sublist_id, $send_list_id );
+							if ( is_wp_error( $segment_data ) ) {
+								return $segment_data;
+							}
+							if ( ! empty( $segment_data['options'] ) ) {
+								$payload['recipients']['segment_opts'] = $segment_data['options'];
+							} else {
+								return new WP_Error( 'newspack_newsletters_mailchimp_error', __( 'Could not fetch segment criteria for segment ', 'newspack-newsletters' ) . $sublist['name'] );
+							}
+							break;
+					}
+				}
+			}
+		}
+
+		// Sync folder selection.
+		$folder_id = get_post_meta( $post->ID, 'mc_folder_id', true );
+		if ( $folder_id ) {
+			$payload['settings']['folder_id'] = $folder_id;
+		}
+
+		return $payload;
+	}
+
 	/**
 	 * Synchronize post with corresponding ESP campaign.
 	 *
@@ -789,15 +1039,8 @@ public function sync( $post ) {
 				throw new Exception( __( 'The newsletter subject cannot be empty.', 'newspack-newsletters' ) );
 			}
 			$mc             = new Mailchimp( $api_key );
-			$payload        = [
-				'type'         => 'regular',
-				'content_type' => 'template',
-				'settings'     => [
-					'subject_line' => $post->post_title,
-					'title'        => $this->get_campaign_name( $post ),
-				],
-			];
 			$mc_campaign_id = get_post_meta( $post->ID, 'mc_campaign_id', true );
+			$payload        = $this->get_sync_payload( $post );
 
 			/**
 			 * Filter the metadata payload sent to Mailchimp when syncing.
@@ -810,6 +1053,11 @@ public function sync( $post ) {
 			 */
 			$payload = apply_filters( 'newspack_newsletters_mc_payload_sync', $payload, $post, $mc_campaign_id );
 
+			// If we have any errors in the payload, throw an exception.
+			if ( is_wp_error( $payload ) ) {
+				throw new Exception( esc_html( $payload->get_error_message() ) );
+			}
+
 			if ( $mc_campaign_id ) {
 				$campaign_result = $this->validate(
 					$mc->patch( "campaigns/$mc_campaign_id", $payload ),
@@ -838,13 +1086,6 @@ public function sync( $post ) {
 				$mc->put( "campaigns/$mc_campaign_id/content", $content_payload ),
 				__( 'Error updating campaign content.', 'newspack_newsletters' )
 			);
-
-			// Retrieve and store campaign data.
-			$data = $this->retrieve( $post->ID );
-			if ( ! is_wp_error( $data ) ) {
-				update_post_meta( $post->ID, 'newsletterData', $data );
-			}
-
 			return [
 				'campaign_result' => $campaign_result,
 				'content_result'  => $content_result,
@@ -1705,8 +1946,10 @@ public static function get_labels( $context = '' ) {
 			'name'                    => 'Mailchimp', // The provider name.
 			'list'                    => __( 'audience', 'newspack-newsletters' ), // "list" in lower case singular format.
 			'lists'                   => __( 'audiences', 'newspack-newsletters' ), // "list" in lower case plural format.
+			'sublist'                 => __( 'group, segment, or tag', 'newspack-newsletters' ), // Sublist entities in lowercase singular format.
 			'List'                    => __( 'Audience', 'newspack-newsletters' ), // "list" in uppercase case singular format.
 			'Lists'                   => __( 'Audiences', 'newspack-newsletters' ), // "list" in uppercase case plural format.
+			'Sublist'                 => __( 'Group, Segment, or Tag', 'newspack-newsletters' ), // Sublist entities in uppercase singular format.
 			'list_explanation'        => __( 'Mailchimp Audience', 'newspack-newsletters' ),
 			// translators: %s is the name of the group category. "Newspack newsletters" by default.
 			'local_list_explanation'  => sprintf( __( 'Mailchimp Group under the %s category', 'newspack-newsletters' ), self::get_group_category_name() ),
diff --git a/tests/test-labels.php b/tests/test-labels.php
index 0a1fdc3a0..87ccb41ee 100644
--- a/tests/test-labels.php
+++ b/tests/test-labels.php
@@ -20,11 +20,11 @@ public function test_labels_inheritance() {
 
 		$ac_labels = Newspack_Newsletters_Campaign_Monitor::get_labels();
 		$this->assertSame( 'Campaign Monitor', $ac_labels['name'] );
-		$this->assertSame( 'list', $ac_labels['list'] );
+		$this->assertSame( 'list or segment', $ac_labels['list'] );
 
 		$ac_labels = Newspack_Newsletters_Constant_Contact::get_labels();
 		$this->assertSame( 'Constant Contact', $ac_labels['name'] );
-		$this->assertSame( 'list', $ac_labels['list'] );
+		$this->assertSame( 'list or segment', $ac_labels['list'] );
 	}
 
 	/**