Who Will Win the SMTP Authentication Wars?

There are three major proposals for SMTP authentication out there. Do we need to decide on one, or can the result actually be two or more? Now that Microsoft has announced Caller ID, the grand experiment can begin.

Probably the single biggest news out of last weeks RSA conference was Microsofts announcement of its Caller ID for E-Mail standard. Caller ID may be the third of the three major proposals that have been announced, but now that Microsoft has put its cards on the table, a great experiment will begin. Over the next year or so, the big players in e-mail—ISPs, software vendors, major corporate users and the government—will see which of them works best.

The three major proposals are SPF, Caller ID and Yahoos Domain Keys. SPF is actually up and running, with (as of Feb. 27) 7,957 domains registered as implementing it (although a large number of those appear to be parked, inactive domains). Caller ID is starting to roll out as Microsoft sets up the Hotmail servers to support it for outbound mail. Hotmail will begin checking inbound mail for Caller ID this summer, while other major companies, including Amazon.com and Brightmail, have agreed to test it too. Domain Keys, to be honest, hasnt even been officially announced, although Yahoo has conducted private briefings all over the place and Sendmail, the famous mail server company, has announced it is working on support for it.

This isnt like three brands of bleach, where youve got the same chemicals in all three bottles. In fact, the more you look at these standards, the more different they look. I had been fearful that having three major standards competing would be discouraging to the market, since explaining even one of them isnt easy. And consider that the three major mail providers in the United States—AOL, Yahoo! and Microsoft—are implementing the three different standards. I think, however, that the three, or at least two of them, could complement each other. The ideal solution may be all three, or some later standard that combines the features of two or three.

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I also think that the vendors involved in these standards arent necessarily going to be hardcore proprietary about their proposals. AOL, which has implemented SPF for outside users to confirm AOLs mail servers (inbound AOL mail doesnt check SPF though), tells me they view this implementation as an experiment. They are not committed to SPF. But the dual problems of spam and e-mail worms had gotten so bad, and SPF was the most mature of authentication standards, that they moved on to the test phase. If some other standard, or combination of standards, proves more effective, AOL wont have a problem implementing it.

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