Fastmail.fm (a paid mail provider) also has a feature to not load remote images, and it’s on by default.

You can also set up arbitrarily complex filtering rules using Sieve, if the built-in rules UI is not sophisticated enough.

To add some more mailbox.org also has it with sieve rules. Posteo should have it too iirc

Long time ago somebody told that gmail pre fetches all images, so tracker pixels report exactly one open occurrence for images in gmail email.

Disabling external images was the default until they started proxying+caching the images themselves. So now _by default_ clients get to see the images without sending tracking data to the senders - Google doesn't like competition.

I still keep the images disabled, though. In most cases, you don't care about what's there in the images anyway.

Mozilla's Thunderbird also has this feature. I'd imagine most security conscious mail reader/browsers do.

So does Apple Mail, for anyone wondering.

It also helps avoid "oo shiny!" distractions and helps keep the focus on the message.