Generally speaking, messages sent out over a LISTSERV-based mailing list
can be identified because the "To:" field points to the mailing list.  For
instance, all messages distributed by LSTOWN-L have "To:
[log in to unmask]".

Alternatively, if subscribers have the "SUBJECTHDR" option set, the name of
the mailing list will appear in the subject of the message as follows:

>Subject: [LSTOWN-L] Re: listserv name in message header instead of
>    sender mail id

You may wish to set the "SUBJECTHDR" option as a default option.  In
addition, you may wish to set all current subscriptions to SUBJECTHDR, or
send mail to the mailing list instructing users on how to do so.

Hope this helps,
jwgh