Substack blames iCloud Private Relay outage for big drop in newsletter open rates

Last week, Apple’s iCloud Private Relay feature experienced a days-long outage. Today, that outage is being blamed by Substack for a troubling trend that its writers observed: a substantial drop in open rates for newsletters sent during the outage. The full truth is a bit more complicated, though.

Substack’s explanation for declining open rates

Per a recent Substack Writers post:

After investigating, our team has determined that the recent decline in reported open rates is likely due to an outage with Apple’s iCloud Private Relay. However, it does not reflect an actual change in opens, as click-through rates have been stable during this time. If fewer people were opening emails, we would expect fewer people to be engaging with them as well, but we’re not seeing that. Secondly, the drop in reported opens is entirely concentrated among Apple Mail users.

It’s important to note that Apple Mail obfuscates opens for many users, making reported opens from Apple Mail generally less reliable than from other email clients. While we understand that open rates are often viewed as key metrics, we recommend focusing on other stable indicators like click-through rates for a more accurate measure of engagement.

References by Substack’s team to Apple Mail behavior is related to Mail Privacy Protection. The underlying tech for this feature is Apple’s iCloud Private Relay system, so the outage affected Mail’s behavior too.

Substack’s explanation, though, has caused confusion for some. Why? Because it leaves out some important details about how open rates are artificially inflated by Mail Privacy Protection.

Inflated open rates due to Mail Privacy Protection

Many would expect that during the recent outage, open rates for Substack newsletters would have gone up, not down. If Mail Privacy Protection was taken offline, it could no longer obscure user activity. Thus, publishers should have seen higher open rates for their messages.

So why did open rates go down, not up?

It’s because the outage meant the numbers were actually closer to the true open rates.

Mail Privacy Protection, because of the way it’s designed, can only keep publishers from seeing email open rates by essentially treating every message like it’s been opened. Even if it never has been.

This leads to inflated open rates, thus Substack’s recommendation that writers focus on click-through rates instead.

The reason this outage was able to have such a big impact is that Mail Privacy Protection is available to iOS users at no extra charge—it’s not part of the iCloud+ bundle of other iCloud Private Relay features.

Mail Privacy Protection can be configured in Settings under Mail ⇾ Privacy Protection ⇾ Protect Mail Activity.

Do you use Mail Privacy Protection, or the other iCloud Private Relay features? Let us know in the comments.