I don't know if my explanation of error delivery messages would be called
definitive, but I'll offer one reason for these messages.  When a message
bounces on the list, the listowner AND the message writer are notified of
that delivery error.  Therefore, if you send a note to a list and only
one recipient on the list can't receive it, you will get a message back
saying that there was an error in delivery of the message.  This does not
mean that everyone else on the list didn't get your message, though.  On
autocat, you may get a message stating that one person could not receive
the message but that doesn't mean 660 others didn't.  Setting your options
to REPRO is a good way to find out if your message did get out.  As for the
errors, the listowner is informed and will take care of the problem if
possible.  Usually it means deleting the address causing the error.  This is
why some of you may get back from a long vacation only to find out you've been
taken off the list!!

Nancy J. Keane
Listowner, Autocat
University of Vermont