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5.5.0 smtp;501 > is invalid or DNS says does not exist

Medium Priority
Last Modified: 2012-05-11
Hi Guys,

We have a 2003 Exchange server and we are recieving the following bounce back when sending mail to a particular external mail server.

"The following recipient(s) could not be reached:

There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <SERVER.domain.local #5.5.0 smtp;501 <SERVER.domain.local> is invalid or DNS says does not exist>

Any help on this would be greatly appreciated and further information will be on hand.

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Do an nslookup and check that has MX record on DNS. Telnet remote mail server on 21 TCP port and check that you can connect.


The DNS checks come back fine for the mail.domain.com and it also returns the correct external IP of the Server.
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Will this cause issues if we were to change the settings:
"You can change the FQDN in your exchange system manager, navigate to your server, then protocols, then SMTP and click the properties of your Default SMTP Virtual Server.

Then choose the tab 'delivery' and click 'advanced'. There you can set your Fully Qualified Domain Name. After you've changed it, please restart the SMTP server (right click, stop, start)
Hope this helps!"

This won't cause any issues. In the unfortunate case it would, you can always set is back to what it was. I have never experienced any problems with this though :)
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