> Is this a listserv problem, our system problem, the subscriber's problem,
> or netcom.com's problem?  Anything I should do as the listowner?
 
I'd say it's the subscriber's problem. There is no guarantee that
foo.com and bar.foo.com are in fact the same machine, or that
users on bar.foo.com are the same as foo.com.
 
> >IOW, I'm probably subscribed as [log in to unmask]
> >My POP mailer produces an address such as [log in to unmask]
 
Probably a sendmail thing -- if the user is submitting an
unqualified address of foo@netcom in the POP setup, the correct
behavior is to append the local domain name and then process the
message. He may want to verify that his POP client is sending
[log in to unmask] in the SMTP envelope transaction. Some older versions
of Eudora used to do this sort of thing.