Your open rates are about to explode and I don’t mean in a positive way.
Apple’s email client, which holds about a 40% market share in a July report, will launch Mail privacy protections with the iOS 15 update, coming in the next month or two. With these protections, Apple will offer users this protection, which most will accept.
Once accepted, any email coming through the Apple mail app (whether derived from Outlook or Gmail or whatever) will go through a process of being completely loaded or cached by Apple. Therefore, any email sent to someone whether opened or not will be counted as opened.
There are a few things that you can do.
Apple and Email Opens