>[. . .]
>Many thanks - that seems to have been the problem:  bounced mail from that
>one address (altho why it wound up with that kind of error message, I don't
>know). [. . .]

Not to beat a dead horse or anything, but here's why you got the message
you did.

The bounce message, apart from being poorly put together, was sent to the
wrong address.  It should have gone to [log in to unmask];
instead it went to [log in to unmask], the mailing list itself.

Were LISTSERV to be poorly-written, that would mean that the bounce message
would be distributed over the mailing list.  This new distributed message
would generate another bounce, which would generate another, and you'd end
up with a big mail loop spewing garbage all over your subscribers.

However, LISTSERV is aware of this potential problem and tries to prevent
it in various ways.  One method it uses is to look for things in the body
of the message that indicate that a message is being forwarded back to the
mailing list (as was happening in this case); for instance, it looks for
"To: Blues Lovers Mailing List <[log in to unmask]>" in the _body_
of the message.

In this case, since the full headers of the bouncing message were quoted,
it found this and other indications that the message was a bounce.

So it forwarded the bounce to you saying that it thought the message was a
bounce and why.

-jwgh