One thing that has annoyed me about receiving email is so-called tracker pixels. These usually 1x1px transparent images that are remotely loaded into HTML email enable the sender to track information about be. A good resource about them is No To Spy Pixels.
As such I’ve tended to run my email clients with remote resource loading disabled, which isn’t the best experience as a surprising number of legitimate email even display the call-to-action link as the CSS styling doesn’t load either.
I use Apple Mail and recently came across MailTrackerBlocker which is an open source plugin for Apple Mail for Mac that blocks the major mail trackers. Obviously, allowing any remote resource to be loaded means that I may be tracked anyway, but it removes the common ones.
So far, I like it and think it’s a reasonable balance for me between not wanting to be completely tracked and living in the 1990s.