I assume you setup forwarding or recipient_bcc_maps for the incoming
-Forwarding being maintained much easier in the admin console/CLI - being stored in ldap/kept through upgrades and what not.
-Though you could always just duplicate the sender off the same file for simplicity.
Just a little forewarning: If you are to delete/lock/close the
manager@domain.com account definitely remove those maps at the same time, as I believe if mail to the BCC address bounces it will be returned to the sender (which would get the original senders confused real fast of course).