Elm's filter equivalents, plz!

I am trying to switch from elm's "filter" to procmail and I find the
syntax confusing and insufficiently documented[?]. I am mainly looking
for Procmail's equivalents for following "filter's" variables:

                    1] %r [sender's address]
                    2] %s [subject]
                    3] %t [time]

My ultimate aim is to design an autoresponder which while placing a copy
of the incoming message in user's "mbox" responds to sender notifying
change in my "domain name" if and only if the sender used the old domain
in his/her address. Currently I have aliases doing the job.

Thanks for suggestions.

Sree.