>I'm assuming that the "relay" error occurs because mail from a
>LISTSERV list uses the list address as the To: line, meaning that
>the server will see that the message is neither from nor addressed
>to any address in its domain, and so assumes it is a relay.

This is probably possible if the server is severely misconfigured,
but I don't _think_ I've seen this happen.

>Is there any standard protocol for servers to identify list mail correctly?

RFC 821 as modified by RFC 1123 lays out how mail gets from one point
to another.

>Should I be referring their postmasters to a specific RFC and
>request them to reconfigure their setup?

Here's essentially what you need to do.

1) Find out what the MXs (mail handlers) are for the domain in
question.  For instance if the bouncing address is [log in to unmask]
you would do an "nslookup -TYPE=MX example.com".  There may not be
any MXs defined in which case mail is handled by example.org itself.

2) For each MX in turn, connect to port 25 (you can usually do this
using a telnet program; from a command line it would probably look
something like "telnet mail.example.com 25") and issue some SMTP
commands to verify what's going on.  You may need to hit 'return' a
couple of times to clear out the stuff that telnet clients generally
send when they first connect.  Then try the following commands:

        HELO lsoft.com [or wherever you're connecting from]
        MAIL FROM:<[log in to unmask]> [your email address goes here]
        RCPT TO:<[log in to unmask]> [the bouncing email address goes here]

If you get an error after this last command, particularly one that
mentions 'we do not relay' or similar, then there's your proof.  At
this point you can send mail to [log in to unmask] (or
whatever the faulty mail relay is) saying that their machine is
defined as a relay for the example.com domain but does not appear to
be configured to accept mail for that domain.  You may wish to paste
in copies of the nslookup and telnet results.

Occasionally you run into problems where a site will accept mail for
example.com but not for EXAMPLE.COM.  This is severely broken
behavior; Internet standards require that the domain part of the
email address be case-insensitive.  You can test for this using a
method similar to the above:

        HELO lsoft.com
        MAIL FROM:<[log in to unmask]>
        RCPT TO:<[log in to unmask]>
        RCPT TO:<[log in to unmask]>

If you get different responses to the two RCPT TO: commands then
there are problems.

If you want to get into this seriously I would download a copy of RFC
821 and look it over.  It's written pretty well, gives lots of
examples, and is in general pretty easy to read.  I believe I got it
from available at http://www.imc.org/rfc821

Thanks,
--
Jacob Haller, Technical Support
L-Soft international, Inc
http://www.lsoft.com/