I want to deliver email to external non-Exchange hosted users. Both the Exchange and external mail server are using the same domain name. My Exchange accounts are able to send to any other domain name, but if I attempt to send a message to externally hosted email account with the same domain name then I get an error. Please tell me what I need to do here.

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3 Answers

You don't mention what version of Exchange you're using so I'll guess 2007 and suggest you look here at what Microsoft calls a shared domain space: http://technet.microsoft.com/en-us/library/bb676395%28EXCHG.80%29.aspx. Note that 2010 does basically the same thing and that while the technique in 2003 isn't quite as great, it works there too.

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I'm not familiar with Exchange - can you explicitly state for a given user that the e-mail must be forwarded on to a different server? I.e. forward all mail to xyz@123.com to the server 192.168.0.1.

Or you could set up a subdomain (e.g. nonexchange.123.com) with the MX records pointing to your non-exchange server, set up xyz@123.com on your Exchange server, and set up a rule on that user's mailbox that will forward all mail from xyz@123.com to xyz@nonexchange.123.com.

The non-exchange user could then SMTP through the Exchange server using their Exchange username/password.

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why not put them on exchange? Is there a reason you can't?

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This would have been a better comment, on the OP's question, than an answer. – jscott Dec 24 '10 at 18:02
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