so we use separate classes to handle different tasks

app/workers/email_receiver_worker.rb

lib/gitlab/email/handler.rb

lib/gitlab/email/handler/create_issue.rb

lib/gitlab/email/handler/create_note.rb

lib/gitlab/email/receiver.rb

lib/gitlab/incoming_email.rb

spec/lib/gitlab/email/receiver_spec.rb

spec/workers/email_receiver_worker_spec.rb