Route images on emails through a proxy, protecting the end-user's IP and User Agent.

Basically, just replace image URLs on images so they start as https://image.com/image.png and turn into https://external-content.duckduckgo.com/iu/?u=https://image.com/image.png.

This should be optional since images routed through DDG could be seen by them, so people who don't trust them for whatever reason should have a way to turn the feature off.

I don't know of any other proxies, is any others exist maybe make it a choice between the various services?