I think there should be an option to enable scanning of emails for viruses and spam before they get to the email forwarder / get forwarded to the final destination server.

What happens is people setup email forwarders, the raw email is then sent to their off site address. If that email is spam or malicious, the destination server ends up blacklisting the server that has the forwarder setup because it thinks the forwarding server was the one that sent the bad emails.

This is not a problem on all RBLs but there are some really bad RBLs like senderbase who list your server for this and they take years to remove you.

It would be nice to prevent a listing at the cost of server resources.

AOL is another one who I believe does this. They are not so hard to get off of their list as senderbase, but again it would be nice to be able to prevent this in the first place.