I totally agree with you.
But unfortunately I've no access at all to the receiver spamfilter.
I know that is not a problem of ISPConfig. But I've access just to the ISPConfig server.
That's why I want to find a way to setup ISPConfig server to avoid the sender IP when deliver the email to the receiver.
Or maybe do you have a better idea?
The filter on the local system should ignore these ip addresses and only use the real sender IP and not any IP addresses that the mail passed on the way to the receiver.
It's using the real sender IP, that is a bad IP (because the ISP is NATing all the users with few IPs)