Since the Pilot shutdown, I have a few people with problems sending to
lists.

The first one was an Outlook user, sending to ~130 students with msu.edu
addresses. Outlook gives an error message similar to "An error occured
while sending mail.  The mail server responded unknown user. "

Apparently the entire message is being bounced because at least one of
students didn't upgrade from Pilot.  We split the list in half, the N-Z
ones were OK, but A-M still gives an error. Still trying to pin down
which of the 65 addresses is a problem.

Today, a prof using Mozilla is trying to send to a class (list of
addresses downloaded from Angel). Same thing happens.

I can't think of any client settings (Outlook or Mozilla) that would
affect this.

Is the mail server really supposed to refuse messages in this manner?

Any thoughts on how to easily identify the problem IDs?

thank you!
-John