I'm migrating from Cyrus/Postfix to Zimbra.

I was proposing to move accounts a few at a time using imapsync, gradually migrating the domain of circa 100 accounts over a period of a week.

When an account was moved I planned to use an entry in /etc/postfix/canonical like:

russell@mydomain.org russell@zimbra.mydomain.org

That's all well and good, but I'd prefer if accounts on zimbra.mydomain.org could email without the zimbra subdomain. I.e. messages sent from zimbra during the migration would look like russell@mydomain.org

If I set up mydomain.org as a domain on the zimbra server I then can't email non migrated accounts at mydomain.org as it tries to deliver their mail locally.

Is there a solution to this issue, or am I going about this the wrong way?