Sharepoint incoming email problem

We have a customer with a Sharepoint site which has been receiving email normally for more than a year.  Nothing on the server has been changed, but today users began reporting that emails to the site are being rejected with the error 550 5.7.1 Unable to relay for <address>.

I've tried restarting the SMTP service, but this didn't solve the problem.

It is a Windows 2008 Server running SharePoint Services 3.0.
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It might very well be due to a hotfix / patch or automatic update... So "something" has probably been "changed" under the hood.

Have you checked your SMTP service's relay settings?

johnny_the_knifeAuthor Commented:
The relay settings appear normal, however, in the event log I am seeing the following error:

Message delivery to the remote domain <domain> failed for the following reason:  unable to deliver the message because the destination address was misconfigured as a mail loop
johnny_the_knifeAuthor Commented:
I think I may have resolved this.  The SMTP server didn't have an email domain alias configured for the address space to which the sharepoint emails are sent.  I added this and it seems to be working.

I have asked the customer to test and I will report back later today.

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