There was some discussion recently, but I don't recall if it was here or
in LSTSRV-L, about mail merge options and having the subscriber details
inserted by way of a Bottom_Banner or other message template.  That
wouldn't give the full header you requested, but it would identify the
original subscriber responsible for your traffic.  And it depends on the
MTA your list host site is using, I believe only LSMTP(tm) provides the
required support.

All the lists on my site use the auto-delete option, so eventually
traffic such as you're seeing would show up with probe info anyway.

>>> [log in to unmask] 1/20/2004 10:33:46 PM >>>
Is there a way to configure a list to reveal the specific address each
copy of a message is sent to? I am in a situation where I happen to be
getting email from one of the lists on my server, but I am not
subscribed to the list. The person who actually manages this particular
list is clueless. The list's header says nothing about which specific
address the messages I am receiving were sent to. I suspect a subscriber
on this particular list has forwarded his or her email to one of the
addresses that I monitor. How can I get that information?

Is my only option to force a probe on that list?