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Stuck in the middle with you: When shared domains are actively risky


What do you do when you're a newsletter publisher or marketing manager sending emails to your list and you run into deliverability trouble through no fault of your own? How do you even know? It's a tricky and sticky situation and I've seen it happen more than once lately, and across more than one email service provider (ESP).

The assumption, most of the time, is that if a mailbox provider -- say, Gmail, decides to put your mail in the spam folder, that it's a reflection of the quality of your mail -- not a reflection of the provider or any issue the provider might be having. Ninety-seven percent of the time, it's all about the (sending) client, not the sending platform. But sometimes it is actually a problem related to the sending platform. And that's not an easy thing to measure. But it's a good thing to ask your local neighborhood deliverability consultant about, because it's happened a few different times now, and I think we're going to see more and more issues like this in the future.

What's going on here? Check out the Venn diagram above, with you, the email sender, right in the middle there. All around you, you're surrounded by the tools to send the mail and the guardians of the inbox. Your ESP or CRM platform that you send the mail from, the blocklists or spam filters (and security filters) examining that mail and mail stream to decide if they think it's good or bad, and the mailbox providers (think Gmail or Microsoft) who accept and deliver the mail, subject to their own filters, AND subject to the third party blocklists and filters that they might subscribe to.

All of these entities have opinions of the others. The gatekeepers, the blocklists and the mailbox providers, in particular, sometimes have opinions about the ESP or CRM tool you're sending from. That opinion could be neutral, it could be positive, or it could be negative. And in some cases, when that opinion is negative, it can negatively affect your ability to get mail delivered. That leaves you “stuck in the middle again,” caught in a deliverability fight not of your own making. You, the sender, can end up with your mail not delivering to Microsoft outlook.com mailboxes because Microsoft has decided to block all mail from that provider (or some shared resource -- certain shared IP addresses, or certain shared domains) and that blocking ends up affecting a significant chunk of (or even all of) the ESP's clients.

The core issues here seem to be related to shared domains and shared domain reputation, mostly driven by list hygiene problems.

If you're an email sender, what can you do? If you're seeing unexpected blocking and you think it's because a blocklist or mailbox provider is filtering mail from your sending platform:

  • Ask your provider about this. “Is there some problem or blocking issue affecting all or many clients right now?” I suspect that most will be honest about this.
  • Give them a chance to address the issue. They know what a pain it is and it's affecting their bottom line, too, not just yours.
  • Ask around. Email marketing groups on Linkedin, Slack, messageboards and mailing lists, anywhere you mingle with other like-minded marketers or email senders. Are they seeing the same thing you're seeing?
  • Test this. It's not always easy to do in an apples-to-apples fashion, but if it's possible to try moving your list over to a different sending platform, implement authentication, and do sample/low volume sending there to compare, consider it. This is risky -- there can be false positive results. Meaning if you truly have a list hygiene issue, a one-off test at another provider might look good, but after a few weeks of sending, it's possible that sending via the new provider will have just as many problems as the old provider.
  • Nudge your provider to properly segregate resources to prevent issues. If a provider allows customization of domains used in messages (click, image, unsub link, etc.), or at least doesn't use the exact same subdomain or domain for the entire client base, that's good risk mitigation.
  • Implement double opt-in. This is controversial, but it's the best way, especially for SMB senders, to avoid “stuck in the middle again” problems caused by somebody else's disagreement. If your lists are clean as can be, the absolute cleanest possible, because of double opt-in, you will side step much of this. And if you have to move providers, you'll be in a good position to do so, data-wise.

If you're an email service provider, what can you do? If you're managing product or deliverability for an ESP platform and a blocklist or mailbox provider seems to be broadly targeting your platform, all or significant chunks of your client base:

  • Segregate shared domain resources. Make sure one single domain is not in use anywhere across the entire client base, in a from address, in a return-path domain, in a click domain, or in an image domain. The issues that people are seeing today are shared domain related, and domain reputation is a big part of the deliverability equation currently. If a block against one single domain means every single client of yours is blocked at ISP XYZ, you've got too many eggs in one basket.
  • Allow clients to configure customized domains or subdomains for as many domain touchpoints as possible. Click, image, from, return-path, etc. If they can make any domains show up as the client's domain, instead of showing up as you, you're both better off.
  • Make it easy for clients to implement double opt-in. And nudge clients (especially smaller ones) toward it. Smaller, less savvy clients are less likely to understand the bigger picture and intricacies of all of this stuff around custom domains or blocklist fights, so think of double opt-in as a sort of vaccine that will inoculate them from many of these risks.

The reason I talk about double opt-in here is because in at least one case, a blocklist provider is using spamtrap hits cross-referenced to shared click-tracking domains for certain providers, and looking to blocklist those domains as a result, causing broad deliverability issues for those clients, even if (I believe) the spamtrap hit counts or list hygiene issues are very minor. This is very much my own personal opinion, but I think the resulting listings -- and deliverability problems that have come from those -- have been a bit of a nuclear overreaction to minor issues (at best) from otherwise good email senders. Whether it's fair or not, any senders in that grouping that were employing double opt-in were likely exempt from resulting deliverability issues.

I realize that not everybody wants to implement double opt-in. As I mentioned in the Small Publishers webinar (where I first talked about this risk and first shared a version of that Venn diagram), it can seem unfair that smaller senders can be subject to more stringent email best practice requirements than larger senders. If a Fortune 50 retailer doesn't have to do double opt-in, why do I? The short answer is, the world is unfair, and a Fortune 50 retailer likely has more resources, and support, to chase after, push back on, and perhaps even make a stink about, an unfair deliverability issue. Somebody much smaller, simply put, does not.

I apologize if any part of this has seemed a bit cryptic. I'm not in the business of name-and-shame, but I did want to continue to warn people about this active, and ongoing, risk. I've got friends and clients affected by these issues and it's not been easy or fun for them. Do what you can to prevent, be aware of, and be ready to react to, issues like this, so that you're not caught unaware and unfairly. And good luck!

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