Wrap List-Unsubscribe link in angle brackets

CHANGELOG

@@ -6,6 +6,7 @@ v 8.13.0 (unreleased)
 
 v 8.12.2 (unreleased)
   - Fix Import/Export not recognising correctly the imported services.
+  - Fix List-Unsubscribe header in emails
 
 v 8.12.1
   - Fix a memory leak in HTML::Pipeline::SanitizationFilter::WHITELIST

app/mailers/notify.rb

@@ -109,7 +109,7 @@ class Notify < BaseMailer
     headers['X-GitLab-Reply-Key'] = reply_key
 
     if !@labels_url && @sent_notification && @sent_notification.unsubscribable?
-      headers['List-Unsubscribe'] = unsubscribe_sent_notification_url(@sent_notification, force: true)
+      headers['List-Unsubscribe'] = "<#{unsubscribe_sent_notification_url(@sent_notification, force: true)}>"
 
       @sent_notification_url = unsubscribe_sent_notification_url(@sent_notification)
     end

spec/features/unsubscribe_links_spec.rb

@@ -11,7 +11,7 @@ describe 'Unsubscribe links', feature: true do
 
   let(:mail) { ActionMailer::Base.deliveries.last }
   let(:body) { Capybara::Node::Simple.new(mail.default_part_body.to_s) }
-  let(:header_link) { mail.header['List-Unsubscribe'] }
+  let(:header_link) { mail.header['List-Unsubscribe'].to_s[1..-2] } # Strip angle brackets
   let(:body_link) { body.find_link('unsubscribe')['href'] }
 
   before do

spec/mailers/shared/notify.rb

@@ -169,8 +169,9 @@ shared_examples 'it should show Gmail Actions View Commit link' do
 end
 
 shared_examples 'an unsubscribeable thread' do
-  it 'has a List-Unsubscribe header' do
+  it 'has a List-Unsubscribe header in the correct format' do
     is_expected.to have_header 'List-Unsubscribe', /unsubscribe/
+    is_expected.to have_header 'List-Unsubscribe', /^<.+>$/
   end
 
   it { is_expected.to have_body_text /unsubscribe/ }