By default, #Thunderbird automatically blocks images in your emails from being displayed -- because many of those images may contain tracking code.
(Sometimes these images are tiny "tracking pixels" you may not even see).
Take your protection one step further by installing #uBlock Origin to block all kinds of unwanted content in your RSS feeds -- it's now an official Thunderbird Add-on: https://addons.thunderbird.net/en-US/thunderbird/addon/ublock-origin/
(EDITED FOR CLARITY)
addons.thunderbird.netuBlock OriginFinally, an efficient blocker. Easy on CPU and memory. uBlock Origin (uBO) is a CPU and memory-efficient wide-spectrum content blocker that blocks ads, trackers, coin miners, popups, annoying anti-blockers, etc. in your feeds.
@Tourma@tech.lgbt@thunderbird
Just added! Very cool.