Back in 2021, Apple introduced a change to how they process every email in Apple Mail.

To improve security and performance, they preload (aka open) the data from every email.

After September 2021, your open rates are inflated. Every email sent to someone who uses Apple Mail counts as an open (even though they may or may not have actually read it).

I have a client who saw her open rates double in 1 month.

But! 

All is not lost.