[exim] exim filters or procmail?

Hello,

May I ask for your advice concerning exim filtering capabilities as
opposed to procmail?

I need to do the following: when a mail comes with a defined subject, I
need to automatically send a new multipart/alternative format email (its
contents is all in one file) modifying the TO field so that it goes to the
sender of original email and changing the subject to something like
"welcome to...". And I need to be able to generate this email with a
current date/time.

Will I be better off learning procmail or can this be handled by exim
filters? Many simple exmaples of auto_info with procmail are based on
sendmail which I do not use.

Thank you very much in advance!

--
Zbigniew Szalbot