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DomainKeys (Tuesday, January 17, 2006)

As I mentioned in an earlier entry, implementing SPF was pretty easy, but implementing DomainKeys was (for now) undoable. This left me in the disappointing situation of receiving regular spam from folks claiming to be various people @yahoo.com. Since Yahoo! has decided not to publish an SPF entry, and the spam messages were otherwise well formed, they were getting through my various defenses. So it occurred to me, that the difference between a legitimate message from Yahoo! and a less desirable one, is that a legitimate message will, of course, have a DomainKey header. Now, I don't have the technology in place to check the validity of the header, but I can certainly check for its presence! So while this is easily worked around by providing a bogus DomainKey, I'm guessing that your average spammer isn't going to bother, since larger domains that check for DomainKeys will actually be verifying them. All I have to do is keep a small list of domains that publish DomainKeys, but don't have SPF entries... and are having their domain name used for spamming. And so far, that list is really just yahoo.com. Problem solved.

—Brian (1/17/2006 1:32 PM)
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