Stuart Colville

Alaska

Muffin

Why don't isps set up a system that checks the IP addresses assigned to internet connections for mailservers on port 25?

There could be a system in place where if you have say an ADSL account with a static IP and you are running a mail server that you submit its hostname and then the ISP will do open relay checks on it.

Other than that ISPs should then block port 25.

As long as there's a way you can get port 25 open if you need it legitimately then that should do it.

The ISP's need to take some action to stop this going on.