[exim] Help with simple .forward filter: accept only campus …

For a class I set up a common email so that the students could
communicate with the TAs. When mail is sent to it, it delivers that
message to the common account and my account, and also forwards that
message to the TAs. The current .forward is just:

\common_account, \my_account, ta1@???, ta2@???

Somehow or other that email address made it onto a spam list. The
common account only needs to receive mail from campus addresses. So I
want to put something like the following in the .forward instead, but
this is pseudocode because I do not know the correct syntax:

# exim filter
if $reply_to = "campus.edu$" then   #reply_to ENDS in "campus.edu"
  deliver common_account   #delivery to addressee on this machine
  deliver my_account       #delivery to 2nd account on this machine
  deliver ta1@???   #forward to one TA
  deliver ta2@???   #forward to another TA
fi
finish

What is the actual syntax for this?

Thanks,

David Mathog
mathog@???
Manager, Sequence Analysis Facility, Biology Division, Caltech