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Is it possible to tell Exchange 2007 to deliver all mail to a certain domain originating from the same domain, to external MX'es even though it is set to handle mail for the domain? I.e. not deliver it internally, but forward it to another MX.


We're in the process of migrating, the official MX is still external, it is only Exchange that thinks it's handling the domain. All users have mail aliases at a second domain (also handled by exchange and with MX records pointing to exchange)

I'd like to keep the MX, but forward all mail for selected users to this secondary domain so that Exchange will handle it, and these select users can access their mail. However, any mail sent to other users in the organization should be sent to the external MX, so it will be accessible at the old server


  • domain1 (primary) is handled by an external server (not Exchange)

  • domain2 is handled by Exchange, however, Exchange believes it handles domain1 as well

At the external server all mail to someone@domain1 is forwarded to someone@domain2 (Exchange). Here both domains map to the same user.

At Exchange, all mail to anyone@domain1 should not be handled internally, but routed to the external server. The trick is that everything is set up at the Exchange server, but users can be migrated one by one, and start receiving mail at Exchange without other users being affected.

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up vote 1 down vote accepted

I don't think this is possible. If Exchange thinks it is the final destination of the mail (if it's an "accepted domain") then it will try to find a mailbox for the recipient. You can set up an "external relay domain" and have the mail forwarded out, but if DNS always tells that mail to come back to you (via the MX record) you will just create a loop.

Docs link:

Edit: Is the other server an Exchange server? If so, you should be able to migrate mailboxes to the other server, and they will be forwarded to the right one.

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Hi, thanks for your reply! The MX is still not pointing to Exchange, so I don't think there will be any loops – grojo Jan 22 '10 at 11:04
OK, I read somewhere "Both Internal and External relay will look internally for a matching address before passing the mail along to the external system.". So your suggestion might not work anyway? – grojo Jan 22 '10 at 11:35
I'm not sure, can you provide more detail in the question, with a bit about the domains, the mail path, etc.? Cheers. – Cawflands Jan 22 '10 at 15:12
I've added some more info, hopefully it makes sense – grojo Jan 25 '10 at 2:35

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