451 Temporary lookup failure

Probably half a dozen times in the last two months I have received this error message from the SMTP server when I have tried to send an email:

The following recipient(s) could not be reached:
xxxxxxx on 12/10/2004 9:57 PM
451 xxxxxxxx@ufl.edu: Temporary lookup failure


I’ve contacted support at least twice about this and received messages both time stating this happens sometimes and should resolve itself.

It looks like this issue has also been discussed here:

Has anyone else received this message when trying to send email through your DH smtp server?