The long tail of domains

I frequently get clients telling me that they have about 15 (20, 30) major domains on their list, and then a long tail of domains with only a couple of recipients. If you sort simply by the left hand side of the @, that’s true.
When you’re sending email, it’s not just the domain in the email address that is important. Of equal importance is the MX. The MX is what actually handles the mail and where many filters are applied. Sorting by MX, instead of simply recipient domain, can identify that most of your small business clients are hosted at a particular provider. The number of subscribers behind that filter may be enough to push that filter into your top 10 or even top 5 recipient domains.
There’s a much smaller tail when grouping recipients by MX domain. It makes it much easier to understand where blocks are happening. I have even seen cases where clients didn’t realize they were blocked at a commercial provider because they only saw the “onesie twosie” domains as undeliverable. They missed a real problem with blocking because they were looking at the wrong data.
I sometimes get the side eye from some ISP folks if I use the term receiver (because, well, they’re senders as much as they are receivers). But I use receiver to help distinguish between the recipient domain and the actual domain handling the email.
When was the last time you looked at your delivery by filter or MX rather than by recipient domain? What did you find?

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I’m not a huge baseball fan, probably a side effect of growing up in a city with no MLB team. SF_giants_ImageBut I do enjoy the social aspects of rooting for local teams when they’re winning big games. Last night I was following the World Series score online and switched over to watch the last inning. I posted something about the game on FB just about 30 seconds before the Giant’s outfield bobbled what should have been a single (at best). I immediately posted an apology, “Sorry about that, shouldn’t have said anything!”
Do I really think that my post somehow cursed two outfielders and caused them to bobble a simple play? No, of course not. But it is a very human response. In fact, there’s an entire advertising campaign centered around the the weird things people do while watching sports.
There is a lot of superstition in email delivery, too. I think that’s a combination of filtering necessarily being a black box, human’s built in tendency to see patterns in random data, and a need to be able to control and affect outcomes.
Figuring out cause and effect in the real world is not trivial. In my research days we set out to control as many confounding factors as possible so we could demonstrate the cause and the effect. That’s really hard to do when you’re not at a lab bench. In the real world, we can’t always control things directly. Instead, we have to rely on statistics and representative (or non-representative) samples.
Delivery isn’t even close to a science and one of the major issues is that filters are always changing. I’ve certainly seen occasions where multiple clients, or colleagues, were having problems delivering to one ISP or another. One of my clients made a change and saw their delivery improve. They patted themselves on the back for figuring out the problem. At the same time, though, other folks saw their delivery improve without making any changes. I can’t always convince people that whatever they did had nothing to do with their delivery improving.
The flip side is I can’t always convince people to stop doing somethings that they don’t need to do. I see a lot of mail with both DomainKeys and DKIM signatures. In most cases both signatures have the same selectors. DomainKeys is deprecated. No one, and I mean no one with a modern email system, is checking DomainKeys without checking DKIM. Senders can safely stop signing with DomainKeys and have nothing happen. It doesn’t matter, lots of ESPs and sender sign with both. They’re not going to change it. I’ve had multiple groups tell me they’re afraid to stop signing because it might hurt their delivery.
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