incoming_email queue has been renamed to email_receiver
I just tried to enable the reply by email feature on our installation, looks like the omnibus default configuration file still has the old queue name:
it has been renamed to email_receiver.
A work-around is to fix this by hand in /var/opt/gitlab/gitlab-rails/etc/mail_room.yml But, after running gitlab-ctl reconfigure, this change will be reset to the default.
This is 8.13.1-ce.0 on Debian jessie.