Okay, I was following this page:

http://wiki.zimbra.com/index.php?title=Split_Domain

to do a split domain for migration.

What I was doing (and tell me if this is wrong, and the correct way to do it if possible) was putting a .forward file in the user directories that were moving.

So we'll use the example.com domain used in the webpage example.

mail comes to user@example.com. The MX points to mail.example.com. So the mail gets delivered to user on mail.example.com. In their home directory they have a .forward that sends the mail to user@zimbra.example.com.

zimbra.example.com bounces with a relaying denied error.

How do I get that mail to user@example.com on the zimbra.example.com server?