On Tue, 17 Apr 2001 12:39:52 -0400, Michael Hensley <[log in to unmask]>
wrote:

>Has anyone else experienced this problem?  I am at a loss as to what is
>causing it.

Most likely the user's ISP is blocking mail with RFC821 MAIL FROM:<> as a
(misguided) anti spam measure.  All OK/Confirm cookie msgs are sent with
RFC821 MAIL FROM:<> (as required by RFC821).

Perform this test:
have the user in question send a msg to   LISTSERV@...  (your host name here)

2 lines in the msg body:

  THANKS
  INFO listname                (insert name of list in question)

This produces 2 responses back from LISTSERV:
--------------
Return-Path: <>
...
From: "L-Soft list server at TRAINING.LSOFT.COM (1.8d)"
<[log in to unmask]>
Date: Tue, 17 Apr 2001 13:39:37 -0400

> thanks
You're welcome!

> info ben2
Information about the BEN2 list is being mailed to you.
--------------
Return-Path: <[log in to unmask]>
...
From: "L-Soft list server at TRAINING.LSOFT.COM (1.8d)"
<[log in to unmask]>

There is no information file for the  BEN2 list. If you have any question
about the BEN2 list, write to the list owners at the generic address:

                     [log in to unmask]
--------------

As you can see, one message is sent with RFC821 MAIL FROM:<> and the other is
not.  If only the second message is received, then you have proof of this kind
of blocking.  Invite the ISP mail admins to read our FAQ on this:
  http://www.lsoft.com/manuals/lsv-faq.stm#5.16
If they continue to want to not follow internet mail standards, then I suggest a
search for a new (standards compliant) ISP.

If both messages are received, then have the user check for unusual mail
filters, etc.