Shutting Down the Highway to Internet Hell
Opinion: The time has not only come for ISPs to block port 25 for consumer accounts, it has long since passed. The rewards for this and other ISP management techniques could be large, but ISPs need to be careful about how they do it and tell usersDo you run a mail server on your home Internet account? If you do, its probably without your knowledge, such as in a mail worm or a zombie spambot. Few if any people running these programs intend to do so, and its time for ISPs to close the door through which they operate. I think theres a consensus developing among anti-spam researchers, many of them responsible for fighting spam on ISP networks, that unrestricted use of TCP port 25 must be shut down to the average Internet consumer. There are those who disagree, but their arguments sound obtuse and defeatist rather than actual justifications to not block port 25. TCP Port 25 is one of the core interfaces of the Internet, through which Internet mail servers typically send mail to each other. Its normal for users to send data out port 25, but they do so to their own ISPs mail server, from which it is forwarded on to the appropriate location. This is the server identified as the outgoing mail server in the mail client configuration.
But if you are infected with a spam zombietypically, a mail worm with a backdoor used by a spammer to cause your computer to send out massive amounts of spamthe mail does not go through your mail server. It probably goes directly to the server of the target domain for the spam message. The overwhelming majority of users have no need to do this and are perfectly well-served by sending all their mail through the ISP mail servers. Its also worth reiterating that the block need only be put on consumer client systems, not on higher-end services.