Mythbusting deliverability and engagement

Yesterday I published an article talking about an engagement webinar hosted by the EEC and DMA. I made a couple predictions about what would be said.

1. ISPs do monitor engagement, even if they do it differently than senders thought.
2. Engagement is important for inbox delivery at some ISPs.
3. Different ISPs have different ways of making inbox decisions.
4. Engagement will matter more in the future.

And, yes, all those things were said. The ISPs told us quite a bit about what they look for when making delivery decisions.
ISPs monitor engagement, measured by what users do with the mail. Do they delete it without opening it? Do they move it from the bulk folder to the inbox? Do they whitelist the sender?
ISPs also measure inactive accounts. Some use the mail to inactive accounts as a metric in their delivery decisions. Some don’t. AOL deletes accounts that haven’t logged in for 180 days. (Personal note: logging into AIM counts as a login and they don’t delete your account if you use AIM.)
Some ISPs use engagement as part of their overall reputation metrics. Other ISPs don’t. Outlook, for instance, doesn’t use engagement other than to make decisions about an individual email and the recipient. At Gmail, however, the individual user actions bubble up and affect the overall delivery of a mail.
This is really one of the first times it’s been so clear to me how different the specifics of filtering are at the different ISPs. I mean, I always knew that they all had their special secret sauce. Recent client experiences have also taught me that what works to get mail back into the inbox at one ISP doesn’t always work for another ISP. Hotmail/Outlook (sorry, I am old school enough I haven’t mentally branded them “outlook.com” yet) treats bounces (user unknowns) as a major factor. Other ISPs use spam trap accounts as a major factor in their decisions.
And, while it was never explicitly said, engagement is not going away as a factor in delivery decisions. Filters and algorithms may change, but senders are going to have to focus more and more on sending the emails people really want to receive in order to get to the inbox.