A quick marketers guide to DKIM

J.D. Falk posted a brief but comprehensive guide to the different DKIM flags: what they mean and how they may affect delivery. (The original link seems to be dead so I reproduced the blog post for reference It’s just that good. A DKIM Primer Resurrected

DKIM only answers two questions:

  • Does the message have a valid signature?
  • If it does, what domain signed it?

The signing domain, identified by the d= tag in the DKIM signature header, is the only part of the DKIM signature where the choices you make now will directly affect the continued deliverability of your messages. This is because d= is how you tell the receiving system who you are.

J.D. goes on to describe the different flags and how they may affect delivery of a particular signed message. It’s a good review of the flags and what they mean.

Irrelevant emails drive unsubscribes
Delivery delays due to congestion

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New Delivery tools

A couple nifty new delivery tools were published over the weekend.
Mickey published Bounce P.I. where senders can paste in an error message or bounce and it will tell you what filter generated it. If the rejection is unrecognized, it will flag the message internally and it will be researched to see if the filter can be identified.
Steve has a new tool at the DKIMCore site. The key generating tool and the record checking tool have been up for a while. This weekend, though, he published a tool to check the validity the DKIM record published in DNS. Tool output shows if the record is valid, the version and the public key.

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DKIM implementation survey

DKIM has been a hot topic of discussion on some of my mailing lists today. One of the open questions is what is holding up adoption of DKIM. I have my own theories, but thought I’d throw out some questions to see how ESPs and ISPs are currently using domain based reputation.
I have set up two surveys one for ESPs and one for ISPs. Responses are anonymous.
I’ll collect responses for a week and share the results.

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AOL and DKIM

Yesterday, on an ESPC call, Mike Adkins of AOL announced upcoming changes to the AOL reputation system. As part of these changes, AOL will be checking DKIM on the inbound. Best estimates are that this will be deployed in the first half of 2009, possibly in Q1. This is something AOL has been hinting at for most of 2008.
As part of this, AOL has deployed an address where any sender can check the validity of a DKIM signature against the AOL DKIM implementation. To check a signature, send an email to any address at dkimtest.aol.com.
I have done a couple of tests, from a domain not signing with either DK or DKIM, from a domain signing with DK and from a domain signing with both DK and DKIM. In all cases, the mail is rejected by AOL. The specific rejection messages are different, however.
Unsighng domain: host dkimtest-d01.mx.aol.com[205.188.103.106] said: 554-ERROR: No DKIM header found 554 TRANSACTION FAILED (in reply to
end of DATA command)
DK signing domain: “205.188.103.106 failed after I sent the message.
Remote host said: 554-ERROR: No DKIM header found
554 TRANSACTION FAILED”
DK/DKIM signing domain: “We tried to delivery your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 554 554-PASS: DKIM authentication verified
554 TRANSACTION FAILED (state 18).”
As you can see, in all cases mail is rejected from that address. However, when there is a valid DKIM signature, the failure message is “554-PASS.”
As I have been recommending for months now, all senders should be planning to sign with DKIM early in 2009. AOL’s announcement that they will be using DKIM signatures as part of their reputation scoring system is just one more reason to do so.

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