Cross forest migration using shared SMTP namespace

[Søren Egtved Lassen]

Hi

I am curerntly designing a migration path from one forest to another,
including Exchange 2003.

The tricky part is that the new forest should hold the same SMTP domain as
the former while migrating

I want to be able to move users gradually and still retain proper mail
delivery from either forest.

I suggest using the SMTP adress space sharing method as described in
http://support.microsoft.com/kb/321721/en-us.

Here is what i would like to do...

For simplicity let's call the old forest "forestA.local" and the new
"forestB.local" and the shared SMTP domain "shared.domain"

On the Exchange server in forestA.local i would change the recipient policy
so the Exchange server is not authoritative for the shared.domain SMTP
domain.
I would then create a SMTP connector that forwards mails for the
shared.domain SMTP domain to the Exchange server in forestB.local.
Restart routing and SMTP services on Exchange server in forestA.local.

On the Exchange server in forestB.local i would change the recipient policy
so the Exchange server is not authoritative for the shared.domain SMTP
domain.
I would then create a SMTP connector that forwards mails for the
shared.domain SMTP domain to the Exchange server in forestA.local.
Restart routing and SMTP services on Exchange server in forestB.local.

For having proper adress list population i would create contacts for the
mail recipients in the opposite forests.

Is this a feasible way of sharing a SMTP namespace while making a gradual
migration?
Would it be better to use the "Forward all mail with unresolved recipients
to host" in either end instead?
What are the risks for creating mailloops, where mails are routed forever?

Any input very much appeciated

Regards

Søren

[Oliver Moazzezi [MVP]]

Hi,

I usually do this once a month and here's what I would do:

Have the domain as non-authoritative as you already suggest on both Exchange
Orgs,
Create the SMTP connector as you mention on each Org to smarhost mail to the
other.
Have the above connector on a bespoke SMTP virtual server, this allows you
to configure the hop count to be alot lower than the default 30. This is the
best that can be done as unfortunately Recipient Filtering doesn't work with
NonAuth domains when the Exchange Server is configured to accept mail for
the domain based on the settings of the SMTP connector (Allow relay to these
domains).

In regards to the GAL, have you tried GalSync (Part of MIIS)? You will get
problems with contacts as RUS stamps the contacts address as a proxyaddress
also - confusing the NonAuth setup.

Let me know if you need to clarify anything,

Oliver