diff --git a/.rubocop.yml b/.rubocop.yml
index 8e5ece231a..4b111e424c 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -16,7 +16,7 @@ AllCops:
     - "db/**/*"
     - "vendor/**/*"
     - "node_modules/**/*"
-  TargetRubyVersion: 3.1
+  TargetRubyVersion: 3.3.6
   NewCops: enable
 
 Layout/FirstArrayElementIndentation:
diff --git a/.ruby-version b/.ruby-version
index ef538c2810..9c25013dbb 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.1.2
+3.3.6
diff --git a/Gemfile b/Gemfile
index bfc1cf9323..96a1aae943 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,7 @@
 source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby '~> 3.1.2'
+ruby '~> 3.3.6'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '~> 7.2.2'
@@ -79,9 +79,6 @@ gem 'jwt', '~> 2.9.3'
 gem 'hcaptcha', '~> 7.1.0'
 gem 'mail_form', '~> 1.10.1'
 
-# set fixed to keep an old version until https://github.com/mikel/mail/issues/1538 is fixed
-gem 'mail', '~> 2.8.1'
-
 # authorization
 gem 'pundit', '~> 2.4.0'
 
@@ -111,6 +108,7 @@ gem 'httparty', '~> 0.22.0'
 gem 'slack-notifier', '~> 2.4.0'
 
 # css styles for emails
+gem 'css_parser', '~> 1.19.1' # dependency for premailer, set to higher version for ruby 3.3 support
 gem 'nokogiri', '~> 1.17.2'
 gem 'premailer-rails', '~> 1.12.0'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 5008d248db..e5da75dec8 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -137,7 +137,7 @@ GEM
       bigdecimal
       rexml
     crass (1.0.6)
-    css_parser (1.12.0)
+    css_parser (1.19.1)
       addressable
     cssbundling-rails (1.4.1)
       railties (>= 6.0.0)
@@ -197,7 +197,7 @@ GEM
       faraday (>= 1, < 3)
     faraday-net_http (3.3.0)
       net-http
-    ffi (1.17.0)
+    ffi (1.17.0-x86_64-linux-gnu)
     flamegraph (0.9.5)
     glob (0.4.0)
     globalid (1.2.1)
@@ -582,6 +582,7 @@ DEPENDENCIES
   capistrano3-delayed-job (~> 1.7.6)
   capybara (~> 3.40.0)
   counter_culture (~> 3.8)
+  css_parser (~> 1.19.1)
   cssbundling-rails (~> 1.4.1)
   dalli (~> 3.2.8)
   datadog (~> 2.8.0)
@@ -609,7 +610,6 @@ DEPENDENCIES
   kramdown-parser-gfm (~> 1.1.0)
   letter_opener (~> 1.10.0)
   listen (~> 3.9.0)
-  mail (~> 2.8.1)
   mail_form (~> 1.10.1)
   memory_profiler (~> 1.1.0)
   minitest-ci (~> 3.4.0)
@@ -650,7 +650,7 @@ DEPENDENCIES
   will_paginate (~> 4.0.1)
 
 RUBY VERSION
-   ruby 3.1.2p20
+   ruby 3.3.6p108
 
 BUNDLED WITH
    2.3.7
diff --git a/app/controllers/repositories_controller.rb b/app/controllers/repositories_controller.rb
index 96180279d5..bc05ca4516 100644
--- a/app/controllers/repositories_controller.rb
+++ b/app/controllers/repositories_controller.rb
@@ -1,5 +1,3 @@
-require 'set'
-
 class RepositoriesController < ApplicationController
   before_action :set_repository, only: %i[show edit update destroy public hook reprocess admins add_admin remove_admin courses add_course remove_course]
   skip_before_action :store_current_location, only: %i[public]
diff --git a/app/policies/feedback_policy.rb b/app/policies/feedback_policy.rb
index a6147ae11f..ec29c28d2b 100644
--- a/app/policies/feedback_policy.rb
+++ b/app/policies/feedback_policy.rb
@@ -1,5 +1,3 @@
-require 'set'
-
 class FeedbackPolicy < ApplicationPolicy
   class Scope < ApplicationPolicy::Scope
     def resolve
diff --git a/test/runners/submission_runner_test.rb b/test/runners/submission_runner_test.rb
index 4ff68b03d7..1065345119 100644
--- a/test/runners/submission_runner_test.rb
+++ b/test/runners/submission_runner_test.rb
@@ -21,8 +21,8 @@ class SubmissionRunnerTest < ActiveSupport::TestCase
 
   STRIKE_ERROR = 'DE HAVENVAKBOND STAAKT!!1!'.freeze
 
-  def evaluate_with_stubbed_docker(obj = nil, **kwargs)
-    obj ||= docker_mock(**kwargs)
+  def evaluate_with_stubbed_docker(obj = nil, **)
+    obj ||= docker_mock(**)
     Docker::Container.stubs(:create).returns(obj)
     @submission.evaluate
   end