We use exhange server 2003 and windows server 2003. iPhones can send and receive emails very well. The pocket PC receives emails from any domain, and can successfully reply to internal emails. However, if an email is sent to an external email address, the message below is received (note that I have used "firstname.lastname@example.org" to replace a yahoo email address. All external email addresses are affected).
From: System Administrator <System Administrator>
Sent: Tuesday, July 07, 2009 1:11 PM
Subject: Message not sent
The message 'RE: test email' was not sent and has been moved to the Drafts folder.
The server returned the following error message:
550 No such domain at this location (email@example.com)
The following recipients did not receive the message: