Add custom headers to invite emails

app/mailers/emails/members.rb

@@ -53,18 +53,10 @@ module Emails
 
       return unless member_exists?
 
-      subject_line =
-        if member.created_by
-          subject(s_("MemberInviteEmail|%{member_name} invited you to join GitLab") % { member_name: member.created_by.name })
-        else
-          subject(s_("MemberInviteEmail|Invitation to join the %{project_or_group} %{project_or_group_name}") % { project_or_group: member_source.human_name, project_or_group_name: member_source.model_name.singular })
+      mail(to: member.invite_email, subject: invite_email_subject, **invite_email_headers) do |format|
+        format.html { render layout: 'unknown_user_mailer' }
+        format.text { render layout: 'unknown_user_mailer' }
       end
-
-      member_email_with_layout(
-        to: member.invite_email,
-        subject: subject_line,
-        layout: 'unknown_user_mailer'
-      )
     end
 
     def member_invited_reminder_email(member_source_type, member_id, token, reminder_index)
@@ -149,6 +141,25 @@ module Emails
 
     private
 
+    def invite_email_subject
+      if member.created_by
+        subject(s_("MemberInviteEmail|%{member_name} invited you to join GitLab") % { member_name: member.created_by.name })
+      else
+        subject(s_("MemberInviteEmail|Invitation to join the %{project_or_group} %{project_or_group_name}") % { project_or_group: member_source.human_name, project_or_group_name: member_source.model_name.singular })
+      end
+    end
+
+    def invite_email_headers
+      if Gitlab.dev_env_or_com?
+        {
+          'X-Mailgun-Tag' => 'invite_email',
+          'X-Mailgun-Variables' => { 'invite_token' => @token }.to_json
+        }
+      else
+        {}
+      end
+    end
+
     def member_exists?
       Gitlab::AppLogger.info("Tried to send an email invitation for a deleted group. Member id: #{@member_id}") if member.blank?
       member.present?

app/mailers/previews/notify_preview.rb

@@ -146,7 +146,7 @@ class NotifyPreview < ActionMailer::Preview
   end
 
   def member_invited_email
-    Notify.member_invited_email('project', user.id, '1234').message
+    Notify.member_invited_email('project', member.id, '1234').message
   end
 
   def pages_domain_enabled_email

spec/mailers/notify_spec.rb

@@ -831,6 +831,19 @@ RSpec.describe Notify do
           is_expected.to have_body_text project_member.invite_token
         end
       end
+
+      context 'when on gitlab.com' do
+        before do
+          allow(Gitlab).to receive(:dev_env_or_com?).and_return(true)
+        end
+
+        it 'has custom headers' do
+          aggregate_failures do
+            expect(subject).to have_header('X-Mailgun-Tag', 'invite_email')
+            expect(subject).to have_header('X-Mailgun-Variables', { 'invite_token' => project_member.invite_token }.to_json)
+          end
+        end
+      end
     end
 
     describe 'project invitation accepted' do