[fetchmail]Messages rejected by Postfix due to antispam rules are not de

Hello,

i´ve setup postfix with header and body checks to remove at least some spam.
What happens is that postfix returns an error code, fetchmail sees the code
and refuses delivery. But the message is not delete from my pop3 server.
They stay there until i log on with the web interface and delete them
manually.

How can i change this behaviour????

Greetings, Joerg