One of my subscribers missed confirmation messages from my LISTSERV
because his ISP was blocking all incoming traffic that didn't contain
a message ID. Their reasoning was that it was an effective way to
trap messages containing the MyDoom worm, which don't contain an ID
line. Unfortunately, LISTSERV housekeeping messages (and digests,
too, I believe) also don't have message IDs. A rather snappy message
came back to me from their support people, asking what the rationale
was for LISTSERV messages not to confirm to the recommendations of
RFC 2822 & RFC 2119. Would anyone care to comment?

--
Michael Quinion