Strip out email body when rejecting email

This prevents pushing large payloads to Redis for the Sidekiq job
arguments

app/workers/email_receiver_worker.rb

@@ -118,7 +118,9 @@ class EmailReceiverWorker # rubocop:disable Scalability/IdempotentWorker
       end
 
     if reason
-      EmailRejectionMailer.rejection(reason, raw, can_retry).deliver_later
+      receiver.mail.body = nil
+
+      EmailRejectionMailer.rejection(reason, receiver.mail.encoded, can_retry).deliver_later
     end
   end
 end

lib/gitlab/email/receiver.rb

@@ -44,6 +44,10 @@ module Gitlab
         }
       end
 
+      def mail
+        strong_memoize(:mail) { build_mail }
+      end
+
       private
 
       def handler
@@ -54,10 +58,6 @@ module Gitlab
         Handler.for(mail, mail_key)
       end
 
-      def mail
-        strong_memoize(:mail) { build_mail }
-      end
-
       def build_mail
         Mail::Message.new(@raw)
       rescue Encoding::UndefinedConversionError,

spec/workers/email_receiver_worker_spec.rb

@@ -37,6 +37,15 @@ RSpec.describe EmailReceiverWorker, :mailer do
           expect(email.to).to eq(["jake@adventuretime.ooo"])
           expect(email.subject).to include("Rejected")
         end
+
+        it 'strips out the body before passing to EmailRejectionMailer' do
+          mail = Mail.new(raw_message)
+          mail.body = nil
+
+          expect(EmailRejectionMailer).to receive(:rejection).with(anything, mail.encoded, anything).and_call_original
+
+          described_class.new.perform(raw_message)
+        end
       end
 
       context 'when the error is Gitlab::Email::AutoGeneratedEmailError' do