I got a similar message from an earlier post. Apparently there's one
address on the list whose host has disappeared. I asked our sysadmin
and he said there's a bug in sendmail that loses the destination that
causes the error. If the problem persists, I'll take the offending
person off the list until he complains. Reposting does not appear to
be necessary.
--Guido van Rossum, CWI, Amsterdam <guido@cwi.nl>
[I'm still thinking about the exception handler syntax...]