>Server at receiving end reports "user unknown."  Global delete of bounced
>address from our lists finds "no action taken."  Is the most likely
>scenario that a user subscribed under one address, had mail forwarded to
>another address without signing off the list, then signed off the second
>address?

That'd be my first guess, particularly if there are repeated bounces.

>Any other scenarios?

It could be that the machine issuing the bounce isn't reporting the
actual email address that the message was sent to for mysterious
reasons of its own.

Alternatively it could be that someone else removed the subscription
before you got to it.  Sysadmin at the bouncing address could have
issued an UNSUB command from the bouncing address, another listowner
could have deleted it, etc....  If you have changelogs enabled you
could search those to see if there's any record of a subscription for
the email address in question.

>Short-term solutions?

Use the SCAN command to find various permutations of the email
address.  If the user's name was included in the bounce search for
variations on that too.  If the email address is from a relatively
uncommon domain (I wouldn't recommend doing this with an aol.com
bounce) you could do a SCAN to find all subscriptions from that
domain and either look them over or do a few searches to see if
there's anything suspicious there.

>Long-term?  Can the manager set all lists to periodic quiet probes?

This is done on a list-by-list basis (though for lists less than a
certain size quiet probing is enabled by default) but this is
probably what I would recommend.

The most effective way to get bad addresses off your mailing list is
to have people renew their subscriptions every so often (Renewal=
Yes).  This may not be appropriate for some mailing lists, however.

If you've got passive probes enabled LISTSERV should find the vast
majority of bad addresses for you.  Of the remainder that you have to
deal with manually it should be possible to figure out what
subscription the vast majority correspond to.  Occasionally you may
run into a bounce which simply does not contain enough information
for you to figure out what the offending subscription is; there's not
much that can be done about this, but fortunately the situation is
very rare.

Thanks,
--
Jacob Haller, Technical Support
L-Soft international, Inc
http://www.lsoft.com/