An email tracker, read receipt and spy pixel blocker plugin for macOS Apple Mail.
MailTrackerBlocker is a plugin for the default Mail app built-in to macOS. Look for the ⓧ button to see which trackers have been blocked. These trackers can track how often, when and where you open your emails. Disabling "load remote content" should no longer be necessary just to read your emails privately!
Download and run the .pkg installer from the link above.
Enable the plugin by (see similar guide for nice pictures):
Disabling "load remote content in messages" with MailTrackerBlocker enabled is redundant; enable both for the best experience.