We're currently running our email infrastructure on the Debian postfix+cyrus packages. We are keen to deploy Zimbra, but I'd like to deploy it with a user-by-user migration strategy. In particular I need to keep our existing systems that we rely on, things like Request Tracker, and mailing lists.

Does this sound possible?

What I have envisaged is a frontend postfix server that routes messages to zimbra based on LDAP mail-routing. In this case the LDAP server would be our existing LDAP infrastructure, not a Zimbra deployed one. So I think it would be easy to deliver email for g8se@example.com to zimbra, but everything else to my existing mail server.

However I'm not sure what we'd do for things like admin@example.com. I would certainly want that to continue going to our existing server, but I'd probably also want emails from the Zimbra server to go to that as well, for instance, for notification of AV alerts. I'm not sure how that would work.

I guess a way to achieve that would be to have Zimbra responsible for @zimbra.example.com email addresses, not for @example.com. Then it would know to route admin@example.com away. However does Zimbra support this secondary sort of role? Am I going to easily be able to configure users so that email emerging from Zimbra is rewritten to @example.com addresses? Or am I starting to create problems for myself?