The North American Network Operators Group (NANOG) conference, a gathering of Internet Service Provider (ISP) engineers and vendors convenes three times a year for mostly technical conversation along with social networking. The recent NANOG conference in Reston Virginia saw some unusually direct talk about Spam and the ISPs that tolerate it from America Online’s Postmaster, Charles Stiles.

Although the usual tone of presenters is either friendly or blankly academic, Stiles’ tone was more aggressive. His message was short and sweet: ISP must change their ways or AOL will blacklist their mail servers. Stile credited ISPs for blocking TCP port 25 amongst their broadband and dialup userbases, a maneuver that has previously reduced spam output. However, he presented data showing that the majority of spam now comes from ISP mailservers directly. As port 25 access has been blocked, the common worms that send out most spam have altered their tactics and have diverted their mail through the various ISP’s own mail servers.

Stile submitted that ISPs must do more than just block port 25 outbound. Ideas included the use of anti-spam techniques on outgoing (as well as incoming) email, the use of outbound email rate limiting, and, most importantly, the implementation of SMTP Authentication for all ISP users.

Stile also addressed the issue of Sender Authentication technologies such as SPF and Sender-ID. While noting that AOL supports these technologies, he was quick to point out that they won’t stop spam coming from other ISPs’ mailservers, as most of the worms send their spam with the local ISP’s domain as the from or sender domain. He also noted that AOL will use published SPF records as the basis for their spam whitelist in the very near future and urged the attendees to register such records immediately.

Needless to say, Stile’s plain talk and hard data were extremely persuasive. ISPs have clearly entered into a new phase of the anti-spam battle where tactics will become more complex and simple measures like Access Control Lists will be insufficient. AOL appears to be quite serious about blacklisting other ISPs who fail to take aggressive enough action against mass emailers. This may result in some partitioning of the Internet mail system in the immediate future if offending mail system operators are slow to act.

Stile’s presentation is available on-line [PDF].