Apple's Mail Privacy Protection ensures that Apple Mail users’ personal information is even better protected.
Mailbutler still works even with Mail Privacy Protection activated.
Mail Privacy Protection masks the user's IP address so that it can’t be linked to other online activity, or used to determine their location.
While Mailbutler does use the IP address of the recipient to show you their location and device type, in general, Tracking still works for you and you can still see if and when your email was opened. The only time the tracking feature is affected at all is IF the recipient uses the latest version of Monterey (or later) AND has Mail Privacy Protection enabled. In this instance, the location and device type of the recipient will be the only information that will be missing.
For more technical details of Mail Privacy Protection, check out this blog post from our CTO & Co-Founder Fabian.