I block all image loading from my email client. Email is a text medium, and inline images rarely add anything useful. I use NoScript and RequestPolicyBlocker to prevent third-party tracking across the web. This breaks many sites until I re-enable permissions, but at least I can make informed choices and grant only the minimum permissions necessary.
The EFF recently posted good report on tracking here:
https://www.eff.org/wp/behind-the-one-way-mirror