I don't think it is the SENDER field that LISTSERV is trying
to SUBSCRIBE, just the FROM field, had the SENDER not been
POSTMASTER userid!  POSTMASTER is a no-no for a SENDER when your
list's keyword is:
 
* FILTER= ALSO,POSTMAST*@*
 
Obviously this person's POSTMASTER is not sending e-mail
and is configured incorrectly, or else all that advice we
have been giving over several years about filter POSTMASTER
would have resulted in a deluge of bounced subscribes.
 
The SENDER, when different from the FROM:, is supposed to
be the software process e.g., NETNEWS, a LISTSERV list name.
POSTMASTER is supposed to be a human being, not a process.
 
LISTSERV did the "right" thing.
 
--  co-owner:   INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
URL:mailto:[log in to unmask]                    "I've been cybertagged :-("