Inverse of sender_reject

I have a requirement to accept mail from user based upon the domain part of the
e-mail address sent in the Mail From Command.

Basically we have mail clients that generate valid e-mail addresses of the form
a.n.other@??? which I'd like to let through our exim mailer.

What I don't want to allow is mail through from some of the students that are
playing with windows 95 and are generating their own e-mail addresses .. and
getting them wrong.. These ones are presently being accepted by our exim MTA
but are rejected by our PP MTA and are ending up queued up on the exim mailer
machine.

I've found the sender_reject command whick lets me do the inverse of what I
want, but is it possible to specify a list of sender mail domains that exim
will accept mail from? or, failing that, configure exim to bounce the failed
mail to our postmaster instead of hanging onto it.

e.g.

sender_accept = " ucc.hull.ac.uk:dcs.hull.ac.uk:......"

As I've got about 20 mail sub domains, a dbm option would be nice.

I'm presently running Vsn 0.56 of exim

any thoughts, help appreciated

alex
Rfc822:A.Sharaz@???
X.400:I=A;S=Sharaz:ou=Computer Centre;O=Hull;Prmd=UK.AC;C=GB
X.500:cn=Alexander Sharaz@ou=Computer Centre@o=University of Hull@c=GB
Sent using Simeon 4.1 over Win-OS2