How come my list of third-party opt-ins from two years ago is now having problems, the question goes. What changed? I'm still doing everything right.
I'm getting that question a lot lately, and a colleague suggested that I post my answer here, to share it with readers.
So, what happened? Why are you getting blocked today, based on utilization of a practice that was considered perfectly acceptable a few years ago?
Keep in mind that ISPs never were really all that keen on allowing in third-party opt-in mail to begin with. Going back for years, if you ever ran into deliverability issues requiring ISP involvement to resolve the issue, they would regularly decline to assist when confronted with an obvious case of mail being sent to third-party lists. But, unless it was obvious, blatant, they didn't always notice. Ultimately, quite a few marketers were able to successfully send third-party advertising emails, keeping complaints low enough to stay under the radar.
But, things have changed since then. Recently, various ISPs have gotten much better at blocking that kind of mail. A whole bunch of squiffy senders who ride the line of permission so close suddenly found their ability to deliver mail take a sharp turn for the worse back in November or December.
Why? Because the ISPs just got smarter. Yahoo, in particular, became much better at figuring out who the co-reg/third-party guys are. Now that they are more easily identified, Yahoo is able to more easily apply policy decisions to this mail. The net is, Yahoo, and other ISPs have clamped down.
Based on that alone, senders are learning that what was OK a few years ago is no longer OK.
Also, keep in mind that an email address isn't forever. The days of just mailing somebody forever until they unsubscribe are gone. Hate it or not, ISPs are looking at engagement rates to identify good vs bad list senders.
What does this mean? ISPs can tell which emails are rarely interacted with, which lists are mostly dormant. If you're sending to a lot of people who never open or click any emails, if you're sending emails that get very few opens or clicks, you're ending up on the low end of the reputation measuring stick, as measured by these engagement-related metrics. The solution is to implement subscriber life-cycle management strategy -- figure out what to do with dormant addresses. (Short answer: stop sending to them.)
"This was a valid opt-in two years ago" is as useless a statement as "my email is CAN-SPAM compliant." They're both true statements, but they no longer have any relevance as it relates to your sending reputation or your ability to get your mail delivered to the inbox.
Permission and deliverability are moving targets. ISPs are constantly stack ranking senders and blocking the ones on the bottom. Eventually, if your practices don't improve over time, and keep up with the times, you're going to eventually find yourself at the bottom of that stack ranking.