ISPs Fighting Back

By Larry Seltzer  |  Posted 2005-04-08 Print this article Print

But some ISPs are putting their feet down, attempting to stop the abuse. At the forefront of this effort, defying all conventional wisdom, is AOL. In the 90s, an era of very different circumstances, AOL was the single largest source of spam on the Internet, and the ISPs reputation suffered terribly from it. Now not only AOL users have high-quality spam control, but AOL is perhaps the most active ISP in terms of policing the use and abuse of mail.

Consider the rules at AOLs "Technical Standards for E-mail Delivery." AOL makes extensive use of RBL services like MAPS so that they know to block spam from open relays, spambots, systems with unsecured form-mail scripts and other spam sources. They actually use the same services to block spam that comes directly from residential ISP clients that should not be sending mail directly; in other words, if you dont block port 25 yourself, they will do it for you.

The ISP goes further—much further. If the sending system does not have a PTR record (a reverse DNS), it is rejected. If a message contains a hex-encoded URL (like http://%73%70%61%6d/), it is rejected. If more than 10 percent of the sending systems messages to AOL bounce, AOL may reject mail from it in general. If a server rejects 10 percent or more of the bounce messages sent to it, AOL may reject further connections from the server. There are other, similar rules.

All of this is intended to use AOLs size and clout to make other e-mail administrators set up and administer their systems properly. In many cases, the reverse DNS requirement, for example, the administrator finds out that he or she doesnt have a reverse DNS because AOL blocks the mail, and the end result is an improvement for everyone. Mail servers should have a reverse DNS if they have nothing to hide.

Perhaps not everyone can do everything AOL does. It does, after all, have a proprietary internal mail system. But theres a lot we can learn from its example. Carl Hutzler, until recently in charge of AOLs anti-spam efforts (he has now moved on to a position in engineering and development of AOLs e-mail), has been evangelizing this ethic of responsibility by mail admins, especially at ISPs.

Hutzler warns of the lazy approach of relying on filters, as so many ISPs do. Its the easy way out. But anyone with a little experience knows that filters dont even come close to solving the problem, although they can be a useful part of the solution. Ive seen messages with overtly pornographic subject lines and bodies make it through three different Bayesian filters. Spammers know how to play with the content of the message to trick filters.

Next page: Port 25, The Nuclear Option

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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