Domain pass-through

[TheDallas]

We are migrating from a hosted MS Exchange solution and what we really want to do is have some accounts on our new Zimbra server and have unmatched recipients passed through to the hosted Exchange box. Is that possible, and if so how?

Thanks.

[mmorse]

Welcome to the forums,
Check out this article: Split Domain - ZimbraWiki

If zimbra is your primary box, aka first in the line to receive mail/the primary mx -
You essentially have to create all the accounts on the zimbra box and on each user set:

zmprov ma user@domain.com zimbraMailTransport smtp:exchangemailserver.domain.com:25

Then when you are ready to move a user from the old exchange system to the new zimbra system -using the exchange migration or whatever method you devise- just run this command:

zmprov ma user@domain.com zimbraMailTransport lmtp:zimbramailserver.domain.com:7025

If your zimbra box is secondary (though I think you mean primary because you said 'passed on through' above) -
Don't waste your time creating all the user's accounts for those still on the exchange system, simply:

zmprov md example.com zimbraMailCatchAllAddress @domain.com
zmprov md example.com zimbraMailCatchAllForwardingAddress @domain.com
zmprov md example.com zimbraMailTransport smtp:exchangemailserver.domain.com

[TheDallas]

Thanks mmorse, that's exactly what I'm looking for.

At the moment the Zimbra box is secondary and since there are a lot of mailboxes on the hosted Exchange box I'd rather not create all the accounts now, but rather create them as the migration progresses.

Is there any downside to using the catchall method?

Thanks again.

[mmorse]

Consider relaying all outbound mail through the exchange box. (also mentioned in that secondary section)

It's off by default, but smtpd_reject_unlisted_recipients cannot be on. (zmmta.cf)
-when enabled this prevents emailing accounts that you don't have, once completed migration I would turn this on as it helps against a ton of spam.
(see here for more anti-spam tips: /forums/administrators/11142-i-dont-think-rbls-bayes-working-me.html#post58026)

Of course also turn off the catchall when your done with migration

[TheDallas]

Unfortunately relaying outbound mail through the Exchange box is not an option - we have no control over it, and I very much doubt the company that provides it will want to punch holes in their firewall to allow that.

The secondary section doesn't say why relaying all mail through the primary is recommended. Is this likely to be an issue?

Thanks again.

[mmorse]

I think you'll be alright, just pay closer attention to the concept of split dns, so that your mail isn't going 'out-then-in'