For those of you who don’t know, DKIM is a form of email authentication. Authentication is a way of proving your email is "authentic" and not a scam (like the kind of email scams that claim to be from your bank, or from PayPal).
High volume email senders (and ESPs) have speculated for the last few years about whether or not major ISPs will begin blocking emails that are not authenticated, and whether or not authentication will help you get your emails past spam filters and into the inbox.
For now, the official word from ISPs is "NO" (interview with Yahoo’s Mark Risher), they will not block non-authenticated emails, per se, but they will mark non-authenticated emails as "potential scams." Or they’ll mark authenticated emails with a little "thumbs up." Basically, using indirect ways to promote more use of authentication.
Here are some other screenshots of how they do it.
So it does behoove senders to authenticate their emails.
And this is why MailChimp comes with free one-click authentication (we’re compatible with multiple authentication formats: DKIM, Domain Keys, SPF, and SenderID). No server setup required.
But will authenticating your email campaigns help your deliverability?
In a way, yes.
We’re colleaugues with a very high volume email sender who is currently having trouble getting emails into Yahoo inboxes. After speaking with Yahoo’s postmaster, they discovered their IPs are blocked by Yahoo, because their emails have generated repeated feedback loop (FBL) spam complaints from the same receivers (here are some articles about ISP feedback loops if you’re not sure what they do).
Everybody knows by now that you should be on all the major ISPs’ FBLs so that you can automatically remove complainers from your list (if you’re using an ESP like MailChimp, we handle that part automatically for you).
If you’re not on their FBLs, and you keep sending emails to the same complainers repeatedly, you’ll eventually get blocked.
Like our friend.
No DKIM, no FBL access
Thing is, our friend uses a "high end" email marketing tool, and it comes with the functionality to clean out FBL complaints. So why aren’t they cleaning out the FBL complaints from Yahoo?
Because the email system doesn’t offer DKIM authentication (unless they pay for an expensive upgrade).
And Yahoo requires DKIM in order to be on their feedback loop (See this blog post over on: Getting Emails Delivered).
No FBL, no inbox.
Since our friend isn’t using DKIM authentication, they can’t get on Yahoo’s FBL, so they can’t see who’s complaining, let alone clean them from their list. So their complaints build up over time, and they get blocked.
The sad part of all this is our friend sends totally legit email, and is an expert at all the best practices (we get a lot of our advice from them).
But without DKIM, they’re left out of the loop.