Port 25, The Counterarguments
Those who argue against ISPs blocking port 25 generally claim that the downsides are high and that spammers will a) evade the blocks and b) easily move to other techniques for sending spam. Joe St. Sauver has made a well-written case for this position. I admire some of his points, but I still disagree with him, and I think half his problem is that he cant see the point through all his defeatism. Namely, even if spammers were to move to other avenues, its still worth closing port 25 to stop them from using it. Getting right to what I feel is the main point, that port 25 blocks will be ineffective because spammers will move to other methods to spread spam, St Sauver brushes aside or ignores counterarguments. He cites recent stories that spammers are beginning to use the ISP mail server instead of sending out spam directly from the client system. There are two counterarguments.If the ISP requires SMTP AUTH (where you must provide a username and password for the outgoing SMTP mail server as well as the incoming POP3 server), then it will not be a simple matter for the worm to send mail. However, since there are programs available that can read the cached SMTP AUTH credentials from popular mail client programs (click here for one thats sold commercially), its not hard to see spam zombies doing the same in the future. They might also do it by monitoring port 25 usage to look for the authentication sequence. In fact, my own ISP, Speakeasy.net, is very lenient about these things. Speakeasy does not require SMTP AUTH for connections made on their internal network (it does for roaming users), but it says that it monitors mail servers carefully and maintains a number of honeypots on active lookout for malware on its networks. I spoke to Speakeasy founder and Chairman Michael Apgar, and he insists that a system exhibiting wormlike behavior will not live for long on Speakeasys network. Within hours the user will be contacted, and if he or she doesnt fix the problem quickly, the plug will be pulled. But Speakeasy is not a conventional ISP; while its happy to sell to anyone, it has a technically more capable audience who pay more for more open services. Apgar is quick to agree that mainstream consumer ISPs should be locking down abusable services, and that port 25 is the biggest problem. Next page: Force the Spammers Onto Official Servers
Check out eWEEK.coms for more on IM and other collaboration technologies.