For some weeks now I get this annoying email from the account under which the
portal is running.

Subject: Invalid messages were generated
Body: The SharePoint Portal Alert service did not send an e-mail message. The
service will try to resend the message.

I can find nothing wrong in any of the portal logs. At first I thought that one
of the users that has set up alerts has become disabled (he/she let the company)
and her/his mailbox was deleted.

Now I’m not so sure…