filtering for lists

Hi folks!
There are few days now i try to use procmail to filtering the messages
to a listproc system.
I want the messages to be formatted in a special way : the subject must
have certain flags and musn't be empty, the message itself mustn't be
larger than a certain size, and so on...
Is anybody of you knows where i can find some infos, or where i can find
exemples of such implementations...

Thanks by advance...

O.M.