[Dovecot] Postfix + Dovecot + Sieve + SpamAssassin

Hello

Until now I used Postfix in combination with Procmail and Dovecot. I am convinced that the Dovecot Sieve plugin is a much more elegant solution.

So I changed to Postfix + Dovcecot Deliver + Dovecot + Sieve. If I understood correctly I cannot call other applications within a Sieve script. Until now I used Procmail to filter Spam Messages with SpamAssassin. Is there a possibility to filter spam messages before/after Dovecot deliver. I want to use the users .spammassassin user_prefs located in their home folder. I suppose if I use a content filter in Postfix this is to early, since the user is not known at that moment. Or am I wrong?

Any help is highly appreciated.

Best regards, Sascha