At 09:41 PM 3/5/2004, you wrote:
>Lately we have been having an increasing problem with people not being able
>to subscribe because they never receive the confimation messages, so they
>can't confirm.  Once we manually ADD them they receive the list mail just
>fine, but they still don't receive any job outputs from LISTSERV,
>regardless of what it is they do, or try to do.

When an SMTP server passes a message to another server, it uses a command
language that, among other things, says where error messages should be sent
(MAIL FROM) and to what addresses the message should be delivered (RCPT
TO).  Here's what a typical MAIL FROM command looks like:

         MAIL FROM:<[log in to unmask]>

If the message cannot to delivered to one or more of the RCPT TO addresses,
an error message will be sent to this address.  The message is still
delivered to the other recipients.  When LISTSERV replies to a command, it
uses a special null form of MAIL FROM:

         MAIL FROM:<>

This means that delivery error messages for any of the recipients will be
discarded.  LISTSERV does this because it has nothing reasonable to do with
the error messages.

Some ISPs are blocking messages with the null MAIL FROM in the mistaken
idea that such messages are spam.  In fact, all delivery error messages are
sent with a null MAIL FROM, so there are many more messages involved than
just LISTSERV's.

About all anyone can do is to contact the sender's ISP and hope for the best.

Roger Fajman