Mail Privacy Protection was announced at Apple's WWDC conference this week. This is a new feature built into the Mail client on macOS and iOS which blocks spy pixels and routes the loading of remote content through a proxy to hide the reader's IP address.

Spy pixels are a common feature of email newsletters. They supposedly help the sender determine whether an email was read or not. This has been used for creepy spying by individuals, but newsletters tend to use them to understand how engaged their audience is.

Email open rate is a key industry metric used to help sell ads. It is also used for list management because sending to users who never open your email is a waste of money. Keeping lists clean is another use of open rates - spam detection will take into consideration whether you are sending email to inactive email addresses, so to maintain a good sender score it is good practice to regularly clean email lists of inactive subscribers.

The problem is that email open rate has never been a good indicator of real engagement. The assumption that a ping to a remote image is a real person opening the email is flawed:

• Security and spam scanning services "open" emails and parse them like real email clients, so can trigger these spy pixels.
• Some email clients load images by default even when the message hasn't been viewed.
• Reading email in plain text means those images don't get loaded. I send all my emails in plain text because it allows the reader to set their own preferences about how they read my messages - client, colors, fonts, accessibility. The Console newsletter has a single image - our logo - with the rest being plain text.
• More and more email clients are defaulting to not loading images, so if the recipient reads the email without enabling those images it is missed from the tracking.
• The fact that someone "opened" an email is not actually an indication that they read anything. It's therefore an inaccurate measure of engagement.

Click rate is the only useful email metric

To understand whether someone is engaged with your newsletter, focus on click rate. This shows that the reader has read the context, found something interesting, and is taking a followup action.

If the purpose of most newsletters is marketing then the goal is always to trigger an action, which has to result in a click.

Newsletters that are purely designed to be read with no further action are more likely to be paid newsletters, so the engagement indicator is not opens or clicks - it's paying. Money is the ultimate indicator of interest, and those who don't want the email will unsubscribe.

The Console weekly developer newsletter has never tracked opens. We don't find them useful because our goal is to deliver interesting tools each week. If someone is interested in the tool then they'll click. If not, they won't. We track these clicks to help us manage the list and to give us an indication of whether our selection criteria are working.

Click rate is the way to measure engagement because it aligns the incentives of the reader (they want to check out something interesting) with the sender (provide interesting content). You get privacy as part of that.

Tools will need to adjust their approach as well. For example, A/B testing subjects often works through using open rate to indicate the engagement. Whether that ever worked is debatable for the above reasons, but now it will have to change.

All the complaints about how this will destroy small newsletters are overblown and a reaction to having their toys taken away. Those toys might be fun, but they're useless. The reliance on this data was flawed in the first place. Perhaps it will actually result in less spam as newsletter owners refocus on content that people actually want to receive.