If I recall, the RFC821 MAIL FROM:<> field userid portion has a "fingerprint" so that if the target mail system "bounces" to that address, LISTSERV(R) will then use the fingerprint to ID the bouncer. I don't recall the format, but to give some concreteness I could imagine a probe on my subscription would be something like (say on LSTOWN-L) MAIL FROM:<[log in to unmask]> At 20:57 10/7/98 -0500, Anne H Toal said: |What does Listserv insert into a message to make it a "passive probe" |(1.8d)?