Postfix, how to filter emails?

Question

postfix

There are:
Postfix, spamassasin.
Spamassasin adds the SPAM text to the beginning of the subject if it has detected spam)
MTA serves several mail domains, users take both pop and imap, authorization as [email protected]
Necessary. How to do it:
1. If SPAM is detected at the beginning of the subject, move the message to the SPAM subfolder (in the maildir) of the user and domain to whom the message was sent. If the folder does not exist, create it. (For imap in a separate folder, for pop in inbox). If the letter was not sent to a specific user of the domain, but received the status in subject - SPAM - move it to the SPAM folders for all users of the domain.
2. In case of unsuccessful checks by the postfix rules of the incoming letter, not just reject it, but also put a message in the inbox of the user (to whom the letter was sent) indicating the reason for rejecting the incoming letter.

Answer 1

1. Read about sieve