Have a zimbra server installed on hostname zimbra.domain.com
zimbra.domain.com is a 2nd ip address on a box witha real hostname hostname.domain.com

zimbra is set to use zimbra.domain.com

have a user called user@domain.com
incoming email works fine

when emails are reeived from ebay. Then postfix reports user@hostname.domain.com cannot be found and bounces.

what is going on?