Open Rates + Deliverability

7th Sep, 2021

Even though we know that email open rates are tricky to gauge, they’re still an incredibly popular metric.

To quickly recap, open rates are inaccurate because lots of email clients block the tracking pixels that allow the open to be tracked. These are blocked in two ways:

  1. Blocking the load of all images, which would present as an unread email
  2. Instantly loading the email on the user’s behalf to strip the pixel, presenting as a read email

In either scenario, the sender has no way of knowing whether the email has been read by the recipient or not.

This is a common feature in lots of email clients and it’s set to become more so as iOS 15 will let Apple Mail users block this tracking.

Business decisions

Open rates are often used to assess how ‘active’ a mailing list recipient is. In other words, do they read the emails?

There is a perfectly legitimate business principle of valuing a small mailing list with high engagement over a large list with very low engagement. Not least because mailing list providers often charge based on the number of users in a list.

The seemingly logical conclusion of these two factors is the practice of removing users who don’t open emails.

In fact, this is something that lots of mailing list providers recommend. Not just for the reasons above, but – according to many providers – sending to many inactive subscribers hurts email deliverability.

Here are some articles on the topic from various providers:

Each of these articles defines different types of inactive subscribers and talks about the impact of keeping inactive subscribers on a list. But there’s absolutely no explanation of how inactive subscribers practically impact deliverability.

How does it work?

The theory seems to go like this:

Gmail, Outlook or another provider see that an email from a sender isn’t being opened by lots of people. At some point, the sender’s emails start to be automatically categorised as spam or sent to Gmail’s Promotions tab.

But how does that work in practice? Gmail or Outlook won’t have access to the open rate data from the mailing list provider (Mailchimp etc).

The only way I can think that this works is that email providers collect their own internal data on email opens. That data is fed back to a scoring mechanism for a sender, or perhaps a universal tool like SpamCop that helps email providers root out spam.

There is a clear case to do this: anyone who had an email account before Gmail will remember how much of a problem spam used to be. Gmail’s filters quickly reduced that headache and spam is no longer a huge issue for lots of email users.

Whose data to trust?

But here’s the interesting thing: email providers such as Gmail and Outlook are likely generating entirely different open rates to mailing list platforms such as Mailchimp and ConvertKit etc:

What’s more, only the email providers decide/impact on what gets delivered to a user’s inbox. They are the ones with accurate data.

Newsletter owners pruning their lists based on open rates run a significant risk of removing active subscribers.

This isn’t to suggest that unread emails don’t impact on deliverability. But – given it’s likely there’s a discrepancy between emails that are reportedly and actually unread – how can a list be accurately pruned?

Some active subscribers will show up as inactive and some inactive subscribers will show up active.

Mailing list platforms cannot tell for certain who is active or not based on open rates alone. It would seem that newsletter owners pruning their lists based on open rates run a significant risk of removing active subscribers.

It might be better to rely on click rates to determine which subscribers are active. Or, even better, remove the spy pixels altogether.

The above makes several assumptions about how deliverability is assessed – if it’s inaccurate, I’d love to hear from you to set the record straight: