Open source plugin for Apple Mail on MacOS, by Aaron Lee:
MailTrackerBlocker is a plugin (mailbundle) for the default Mail
app built-in to macOS. Email marketers and other interests often
embed these trackers in HTML emails so they can track how often,
when and where you open your emails. This plugin works by
stripping out a good majority of these spy pixels out of the HTML
before display, rendering the typical advice of disabling “load
remote content in messages” unnecessary.
Browse your inbox privately with images displayed once again.
There’s a simple installer to download, and the project’s GitHub page has instructions for installing via HomeBrew. I’ve been running it since Wednesday, and it seems to do just what it says on the tin — it blocks many (most?) marketing and newsletter trackers without requiring you to turn off all remote images. When it does block something, there’s a very subtle indication — the small “ⓧ” button turns blue. Click that button and you get an alert telling you what it blocked. Simple and unobtrusive.
MailTrackerBlocker is a cool project Lee has made available for free, but he has a sponsor page where you can send some dough to thank him. (I sent him a one-time donation via PayPal — you should too if you dig this as much as I do.)