On Mon, 18 Dec 2000 14:10:29 PST, Peter Rauch <[log in to unmask]>
wrote:

>If this is what's happening in our LISTSERVer case with MSN (i.e.,
>if MSN doesn't accept LISTSERV's RFC821-conformant command), it
>seems like multitudes of other LISTSERV users around the world
>with "email.msn.com" addresses would have been impacted by MSN's

There is a very simple test to check for blocking of mail with RFC821 
MAIL FROM:<>:

Have the user experiencing the problem send the following command:

To:   LISTSERV@host_name

Message Body:   THANKS
                INFO listname      (use name of list in question)

There should be 2 responses:

one will be like this:   

 Return-Path: <>
 Date: Mon, 18 Dec 2000 15:57:34 -0700
 From: <[log in to unmask]>
 Subject: Re: Information about the TEST list
 To: Ben Parker <[log in to unmask]>

> thanks
You're welcome!

> info test
Information about the TEST list is being mailed to you.

The other will be like this:

 Return-Path: <[log in to unmask]>
 Date: Mon, 18 Dec 2000 15:57:34 -0700
 From: <[log in to unmask]>
 Subject: Information about the TEST list
 To: Ben Parker <[log in to unmask]>

There is  no information file for  the TEST list.  Here is a copy  of the
list "header," which usually contains  a short description of the purpose
of  the  list, although  its  main  purpose  is  to define  various  list
configuration options, also  called "keywords." If you  have any question
about the TEST list, write to the list owners at the generic address:
...


As you can see, one msg is sent with Return-Path: <> and the other is sent (like
all normal list mailings) with Return-Path: <[log in to unmask]>
which is non-blank.  Based on which msg(s) the user gets back you can determine
if mail of the form Return-Path: <> is being blocked.  

(Note: some ISPs do block this but intermittently, or some of their mail servers
may block it and not others....)