[Mailchimp] A newsletter may appear as "sent" when it's stuck "sending"

[miguelpeixe]

For a number of reasons, a Mailchimp campaign can get stuck on "sending" status: https://www.contentmarketingup.com/mailchimp-campaign-stuck-sending/#:~:text=MailChimp%20campaigns%20may%20get%20stuck,technical%20problems%20or%20server%20limitations.

MailChimp campaigns may get stuck on sending due to various reasons: incomplete setup or missing information, non-compliance with MailChimp’s guidelines (e.g., spam regulations), and technical problems or server limitations. Common issues include improper campaign settings, problematic email content, and congested server traffic.

The plugin assumes the newsletter will be sent if Mailchimp returns a successful response from the "send" request.