Scanning already recived mail

[Sephiroth81]

Hello. I've added some new rules to my Spamassassin. All users have Spam folder in their maildir. Is there any way I can scan their maildir so when any mail that they have in mailbox matches against new rules it is automaticaly moved to their Spam folder(i'm not talkin about scanning mail that they will get but mail that they have already recived). I can't bother users to move spam manualy to their spam folder and then use sa-learn). Is there any other way to do that ??

(Sorry for my english :/)