Spammers Most Likely Users Of E-Mail Authentication

Spammers are continuing to adopt Sender ID and Sender Policy Framework, two of the prominent e-mail authentication schemes that are actually intended to stop spam.

Gregg Keizer, Contributor

July 11, 2005

4 Min Read

On the eve of an industry summit to discuss how e-mail authentication can stem the flood of spam, one security firm says that spammers are already using the protocols -- to slip their junk mail past filters.

According to Denver-based message security vendor MX Logic, spammers are continuing to adopt Sender ID and Sender Policy Framework (SPF), two of the prominent e-mail authentication schemes that are actually intended to stop spam.

MX Logic tracked a sampling of 17.7 million messages that passed through its servers from June 19 through June 25, and found that of the 9 percent from domains with published SPF records, 84 percent was spam. Of the even smaller number of messages from domains with published Sender ID records (just 0.14 percent), 83 percent were spam.

"Spammers continue to leverage SPF and Sender ID with the intention of making their messages appear more legitimate," said Scott Chasin, MX Logic chief technology officer, in a statement.

All e-mail authentication schemes work in similar fashion -- by relying on DNS records, either to obtain sending mail server addresses or public keys for decrypting a digital signature -- and are designed to reduce or prevent "spoofing," the spammer and phisher tactic of forging e-mail From: addresses.

Microsoft recently reworked its free-of-charge, Web-based Hotmail service so that all messages not using Sender ID are identified as such. The Redmond, Wash.-based developer isn't, however, deleting non-Sender ID mail or trashing it by placing it in a junk mail filter. Yet.

"As adoption of Sender ID and SPF records grows, and the lack of a domain with an SPF record becomes the exception to the norm, we may choose to investigate unauthenticated e-mail more closely before deciding whether to deliver it to the users' inbox," said Craig Spiezle, a director in Microsoft's safety group, when the move was announced in late June.

MX Logic's Chasin saw a connection between spammers using SPF and Sender ID and the Hotmail move. "[Spammers are trying to] avoid having their messages delivered with an onscreen notification that a Sender ID record was not found, a method Microsoft recently announced it will use on Hotmail," he wrote.

That spammers have rushed to adopt sender authentication isn't the only concern for the protocols. On Monday, the Message Anti-Abuse Working Group, an industry group that includes AOL, Yahoo, Symantec, and EarthLink, released a report detailing a six-month evaluation of SPF and Sender ID. The report acknowledged problems with the protocols when forwarding or re-sending mail, and noted that no authentication scheme can guarantee a message really does come from who it says it came from.

"At best, SPF and Sender ID are comparable to a license plate issued by a foreign country: they show that the vehicle is permitted to drive in that country, but make no indication as to whether that country's regulations are similar to yours, and we can only assume that the driver inside is permitted to use that vehicle," the report concluded.

Also on Monday, Yahoo and Cisco submitted their combined authentication standard, DomainKeys Identified Mail (DKIM) to the Internet Engineering Task Force (IETF) for consideration as a standard. The DKIM protocol, which borrowed bits from both Yahoo's DomainKeys and Cisco's Internet Identified Mail, was first announced in early June. It's expected that DKIM will be discussed at the IETF's Paris meeting July 31 through August 5.

On Tuesday, a collection of e-mail analysts, providers, and users will meet in New York for the Email Authentication Implementation Summit 2005, where Sender ID, SPF, DomainKeys, and DKIM will be put under the microscope. Microsoft, for instance, will be presenting results of its six-month use of Sender ID, while Bank of America will talk about authentication in online banking.

In other e-mail and spam news, MX Logic said that in June zombies accounted for a record 62 percent of all spam. In comparison, May's tally was 55 percent, and April's 44 percent. "The continued proliferation of zombie PCs has levied a heavy cost on ISPs and end users," said Chasin. "Compromised PCs have resulted in millions of users being unknowingly blacklisted, often through no fault of their own."

And the once-vaunted CAN-SPAM Act continues to be ignored by spammers, said Chasin, who noted that just 4 percent of all unsolicited mail in the first half of 2005 complied with the federal legislation. Since CAN-SPAM went into effect in January, 2004, compliance has averaged around 3 percent, with a high of 7 percent in December.

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