Ok. So now I have my Zimbra server up, and talking to the world (I have 2 gateways to separate networks, and I put it behind the NAT filewall that's on the faster one; my MailScanner/Exchange 5.5 setup is on the slower one).
The next step is to teach Z that my Exchange server is its pass-through target, and then manually send it some emails,and make sure they pass through.
The impression I have is that I need to do that by a) telling Postfix it owns the domain (which Z should have already done) and b) putting manual forwards in to *some* file somewhere for each mailbox name (or is it "email address"? We have some aliases) to tell it to pass through.
If I'm reading this page correctly, it's saying that I have to provision *all* the mailboxes and aliases on Z before I can splice it in; the first step makes the mailbox on Z, and the second one tells it to pass through.
Then I back the mailboxes out one at a time, switching the mail and then running the migration wizard.
Do I have that right? ;-) It's not at all clear on that wiki page whether the writer's use of "primary" and "secondary" have to do with which machine talks to the internet and forwards to the other; I'm assuming the "primary" machine is the one which receives directly from the Internet at the domain's MX address.
FInal question, for extra credit.
If I have to migrate *back*, how do I migrate the mail *out* of Z back into Exchange? (NO one ever seems to think about that...)