Your open rate is lying to you (thanks, Apple)
If your open rates jumped in late 2021 and never came back down, congratulations: you didn't get better at subject lines. Apple happened.
Mail Privacy Protection (MPP), on by default for Apple Mail users since iOS 15, pre-fetches every email — including the invisible tracking pixel that "counts" an open — whether or not a human ever looks at the message. To your analytics, every one of those pre-fetches is an open.
Apple Mail sits around half of all email client usage. Which means a large fraction of your "opens" are Apple's servers being polite, not people being interested.
What this breaks
Open rate as an engagement metric. A 45% open rate on a list heavy with iPhone users might be a genuinely great 35% — or a mediocre 20% wearing machine inflation. You can't tell from the number.
Open-triggered automation. "If they didn't open in 3 days, resend with a new subject line" now mis-fires constantly: MPP users look like they opened everything. Same for "send at each subscriber's typical open time" — Apple's pre-fetch time isn't your reader's coffee time.
Sunset policies keyed to opens. The dangerous one. If "engaged" means "opened recently," MPP users look eternally engaged — and you'll keep mailing people who checked out a year ago, which is exactly the complaint risk sunset policies exist to remove.
What opens are still good for
Don't delete the metric — demote it. Opens remain usable as a directional, within-list signal: comparing subject line A vs B in the same send (the inflation hits both arms roughly equally), or spotting a sudden drop (machine opens don't disappear on their own — a real drop usually means a deliverability problem, and that makes opens a decent smoke alarm for inbox placement).
What opens can no longer do is serve as your definition of engagement or your benchmark against industry averages.
What to measure instead
Clicks. A click requires a human finger. Click rate (and click-to-delivered) is the honest replacement for opens in nearly every decision opens used to drive — including who counts as "engaged" for sunset and re-engagement rules.
Replies. Undervalued because they're awkward to track, but a reply is the strongest engagement signal in email — mailbox providers weigh it heavily too. (Related: send from an address that accepts replies. no-reply@ throws away your best metric and a positive reputation signal in one move.)
Conversions. The metric your email program actually exists for. If you can trace a send to signups, purchases, or logins, everything else is intermediate.
The negative signals. Bounce and complaint rates were never distorted by MPP and remain the ones that decide whether you reach the inbox at all.
The bottom line
Opens didn't become useless — they became a machine-inflated proxy that's only safe for relative comparisons. Anchor your definitions of engagement, your automations, and your sunset rules to clicks, replies, and conversions, and treat a falling open rate as a deliverability alarm rather than a copywriting critique.