Its hard to blame Comcast for beginning, as the Washington Post reported, to block port 25 on systems on their network that appear to be spammers. Everyone knows that a huge amount of spam is sent through broadband client systems that have been taken over—through backdoors—by spammers—zombied—and nobody has more broadband clients than Comcast.
While this move costs money and is potentially troublesome for Comcast, slowing down spam is not the only upside to doing this. The article claims that the change has brought about a 20 percent reduction in spam. Assuming that means 20 percent of the spam coming into Comcasts system, thats a lot of freed-up bandwidth.
Since spam makes up at least 50 percent of all e-mail, a 20 percent reduction in spam translates into a more than 10 percent reduction of overall mail, increasing the quality and reliability of that e-mail. And of course its an improvement for even those of us not using Comcasts network because a lot of those zombies send spam to us.
Im no big fan of Comcast, being a victim of their cable TV service, but their cable modem service is probably the best broadband deal for most people who have it available. I have to admire any steps they take to improve it, and this one isnt an easy decision. Comcast isnt typically a bunch of fascists when it comes to enforcing their rules. Its a violation of your Comcast agreement, for example, to run a mail server, but they havent been going around enforcing those rules. So I dont assume that they will suddenly swing over to abusive enforcement.
Within a couple years there will be widespread adoption of one of the emerging standards for SMTP authentication, perhaps the MARID specification currently under development by an IETF group. This will help to prevent spam from getting through to recipient mail servers, but its still going to be worth it for ISPs like Comcast to try to block spamming systems. If they dont, the mail still goes out and burdens the recipient servers into having to block it as unauthenticated. Both approaches are useful for cleansing the Internet of spam.
Next page: After authentication …
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Even after SMTP authentication is in place Internetwide, ISPs still must be vigilant about mail abuse. Authentication wont end spam, it will just end spoofing. (Yes, there are arguments about this, but I think basically it will end that aspect of the spam problem.)
Spammers will likely increase their use of cheap domains to send authenticated e-mail. (Incidentally, theres an inevitable source of future controversy. Services like ZoneEdit will become essential to spammers who want to operate using cheap but legitimate ISP accounts in the west. Should they ask no questions?)
Scott Petry, Postinis founder, has been speaking lately about the declining effectiveness of content scanning and the inevitable rise of IP-based scanning. In other words, its getting harder for automated scanners to tell by looking at the content what is spam and what isnt. Spammers are getting better at making their spam look, superficially, like normal mail. What you have to do is look at the mailing techniques and the network sources of the message. Blocking port 25 at the client end is a brute-force manifestation of this philosophy.
As the Washington Post article makes clear, Comcast is far from alone in this practice, and you should expect eventually that almost all ISPs will jump on the bandwagon. For a company like AOL its even easier, since their own mail services dont use port 25. Port 25 abuse is so rampant on the Internet that ISPs should probably go further.
Ideally I think I agree with George Webb, a group manager of Microsofts anti-spam unit. According to the Washington Post article, “[Webb] thinks port 25 should be blocked by default, and customers should be required to apply for an exception.” If youve got legitimate reasons to run port 25 services independent of those provided by the ISP and you have nothing to hide, the ISP should know about them. If you have privacy concerns with this, welcome to the 21st century.
Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983.
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