I know this is not specifically a zimbra question but I'll run it by everyone anyway. I did post on a postfix specific forum and no one has yet taken a whack at it.
I'm currently migrating our users from an old postfix/imap server to zimbra. I was hoping to forward the mail on an individual user basis by either switching their virtual alias in the postfix/mysql table or some other method so that I can at least move the first few users and work out the issues related. There is no need to move the old mail, just forward the new mail by user.
(As a side note, changing the alias in the table from user to email@example.com@newserver.internaldomain does send the mail on to the new server at which point the user is not found and it is relayed back to the original resulting in too many hops.)
I'm hoping someone has a suggestion because the new server is working perfectly and using the old one as an outbound relay without issue. In theory, it doesn't seems like it should be a difficult thing to do.