Email rejected: Name or service not known


In the last day or so, we start getting our emails rejected by a certain domain with the following message:

I'm sorry to inform you that the message below could not be delivered.
When delivery was attempted, the following error was returned.
 Name or service not known.

The problem is that I don't know on which side is the "name or service not known".

We were able to send a couple of days ago.

Thank you so much for your help!
Alan DalaITAsked:
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Simon Butler (Sembee)ConsultantCommented:
That isn't an Exchange NDR. Therefore I would suspect it is the remote side.
It could be that they have filtering in place blocking your messages. Could also be that their DNS records are wrong. The telnet test is usually a good start, you could also try some of the SMTP tests that are on the internet to see whether a similar NDR is returned from them. If not, that would suggest the problem is with your IP address which they are rejecting.

Dave BaldwinFixer of ProblemsCommented:
I suggest you contact them from another email like Gmail if you have one and ask what's going on.
Dr. KlahnPrincipal Software EngineerCommented:
Telnet into the email server for the remote domain on port 25.  Then initiate an SMTP exchange or ESMTP exchange and see what the server says.

Microsoft has an information page on how to do this, though I would use the simpler HELO command rather than EHLO.

This will tell you whether the problem is at your end or their end.
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