I think it would be interesting to know first of all, from which service is this email being sent from. It can be Metadata, Web, a SAS job, environment manager, I do not know. It might be the case that one of those services has an old configuration.
I would suggest to track down this email from destination to source, meaning:
From the time, you can ask also your mail administrator when this email was sent, and if there is any additional information about its source.
With that information, a system admin could go to the SAS server, to the host, and check in the OS log, about this email sent. Probably there is more information there, about the exact service that sent the email, or a hostname that has not been reached.
At this stage, it should be possoible for your and your admins to identify: the failing hostname and why, the service who tried to send this email, and then you could check the exact configuration of that service and to fix the problem and any other possible underlying problems, if any.