Contact the postmaster.  I think UN*X systems are prone to this
kind of misconfiguration/problem (having to do w/ permissions).
PMDF is also one of those strange animals.
 
Do you check the SMTP port (assuming it wasn't MXed) or perhaps
FINGER.
 
(NB to newbies: e-mail delivery tends to be asymmetric i.e., just
because you can send e-mail, does not mean that others can send
(successfully) to you.  Also, just because you can e-mail someone
doesn't mean that LISTSERV Distributions won't have problems (since
LISTSERV Distribute may choose a different path) or that your
distributions will be delivered consistently.)
 
/Pete