A typical Mutt configuration relies on the entry for text/html in ~/.mailcap. It's quite common to use lynx for rendering, as in the following:

    text/html; lynx -dump %s; nametemplate=%s.html; copiousoutput

Since lynx doesn't load images, that would be safe from this kind of tracking. But another configuration using a different renderer might allow it.

Furthermore, it is also possible to prefer the plaintext version of an email if there's a choice. From my ~/.muttrc:

    alternative_order text/plain text text/html

I can't remember ever being put out by not being able to read messages that fetch images from the web. Even if I have to open a URL, I do it in Firefox, where I run RequestPolicy.