Migration issue with split domain & multi-servers

[adminsmc]

Howdy,
We're migrating from an iPlanet (SunOne) ver. 5.2 emai/calendar system to
Zimbra (latest network version.) We'll be running a split domain with iPlanet as the primary server and zimbra as the secondary.
Currently email routing for *@example.com through the zimbra MTA seems correct. If the user is found locally, email is delivered to zimbra and if not, it's forwarded to iPlanet and if the user is found, delivered there.
My question/issue/problem is that we're going to adjust the forwarding
address of our migrated, iPlanet users to the newer Zimbra MTA for delivery
from the other direction. However we get a bounce sending mail to
user@zmta.zimbra.com and it simply bounces back. (Note: zmta is the name of our zimbra mta host.)
Can I or Should I create a "domain alias" for example.com such as "migrate.example.com" so that our forwards from the old system to zimbra can get through cleanly? If I use the hostname of the zimbra mta server postfix tries to deliver the mail locally. An aliases file on the mta requires local accounts be created and that's out.
Any thoughts or help would be great,
Thanks,
Doug

OS: RedHat ES 4. whatever's the latest
Zimbra: 4.0.4 Network Edition (latest also)

iPlanet config: iplanet.example.com (single box, web,imap,pop,smpt,cal)

Zimbra config: zmail.example.com (store, logger, web, imap, pop)
zldap.example.com (Zimbra LDAP)
zmta.example.com (Zimbra MTA, AV, AS)

[phoenix]

Does this split domain document help?

[adminsmc]

I used the split-domain doc to set things up as I have them (well, plus the multi-server install doc first.) The SD doc explains the logic quite well and addresses the functions to make things work overall but it missed some specifics (in my view.) Of course my view is warped and often wrong.

For example I'll demonstrate some flow issues with SD I ran into -
example.com DNS MX=mail.example.com (consider this our current iPlanet)
mail.example.com accepts all mail for example.com.
foo@example.com
bar@example.com

Now I want to add Zimbra into a SD config with mail.example.com first and the new zmta.example.com as a secondary destination.
*This requires no DNS changes (or should it have?)
* zmta.example.com will accept mail for example.com and forward over to
mail.example.com if the user isn't found.
* mail.example.com will have a per-user forward set to zmta.example.com (but NOT user@zmta.example.com because postfix routes that to local users on zmta.example.com)

So the question came down to...how to forward someone's mail from mail.example.com to zmta.example.com *all* for email addressed to user@example.com ? I'm explaining it poorly but I believe that along with all of the above I need to create a domain alias (migrate.example.com) on zmta.example.com which is aliased to example.com on zmta.example.com.
*whew*
The result being, on mail.example.com I set a forward for user "foo" to foo@migrate.example.com (with an appropriate MX record for migrate.example.com->zmta.example.com) which will route the mail and then (because it's an alias) flip the mail to foo@example.com on the zmta.example.com server.

Am I re-inventing the wheel here or am I clunking along on square wheels because I missed how to round them out?
Thanks,
Doug

[adminsmc]

I'm going to chalk this up to my lack of postfix experience and trying to use
iPlanet terminology/functions with Zimbra. Here's what I concluded.

1) Follow the split-domain setup with zimbta mta second.
2) Create a domain alias for the zimbra mta to accept mail for migrated users
which is *not* the same domain as we're trying to migrate.
3) Create an MX record for the domain alias pointing to the zimbra mta.
4) Forward mail from the legacy mta users to the aliased domain.

Example:
Before -
domain: example.com
MX: example.com mailhost: legacymta.example.com
users: foo@example.com, bar@example.com

After:
domain: example.com
MX: example.com mailhost: legacy.example.com
migrate.example.com mailhost: zimbramta.example.com
zimbra config:
domain: example.com <--- target for end of migration
domain alias: migrate.example.com <-- interim alias for migration
users: foo@example.com <--- migrated to zimbra

Legacy config: <--- will go away after migration
domain: example.com
users: bar@example.com <-- not migrated
forwarded user: foo@example.com forwarded to foo@migrate.example.com

Commands performed on zimbra to enable split domain handling with
the zimbra mta second.
zmprov md example.com zimbraMailCatchAllAddress @example.com
zmprov md example.com zimbraMailCatchAllForwardingAddress @example.com
zmprov md example.com zimbraMailTransport smtp:legacymta.example.com
zmprov mcf zimbraMtaRelayHost legacymta.example.com
zmprov mcf zimbraMtaDnsLookupsEnabled FALSE

Create the domain alias on zimbra.
(*this is a one-line command, split for readability*)
zmprov cd migrate.example.com zimbraDomainType alias \ zimbraMailCatchAllAddress @example.com \ zimbraMailCatchAllForwardingAddress @example.com


Conclusion:
Mail sent to the migrated user foo@example.com via
legacymta -> forwarded to foo@migrate.example.com -> MX Checked ->
to zimbramta.example.com -> aliased to example.com ->
delivered to foo@example.com on zimbra.

zimbramta -> delivered to foo@example.com on zimbra.

Mail sent to non-migrated user bar@example.com via
legacymta -> delivered to bar@example.com on legacymta

zimbramta -> not found locally, forwarded via catchalladdress to ->
legacymta.example.com -> delivered to bar@example.com on legacymta

*When migration is complete, the migrate alias can be removed *and*
MX records can be set to zimbra for example.com *and* we can adjust/remove the forwarding/catchalladdresses *and* enable DNS lookups.

Doug