I use claws on some machines (it has a different set of annoyances than Thunderbird) and it has the feature to pull senders' images from https://www.libravatar.

I use claws on some machines (it has a different set of annoyances than Thunderbird) and it has the feature to pull senders' images from https://www.libravatar.org/ https://www.libravatar.org/ . The occasional mailing list participant gets an image that way and, amusingly, the occasional spammer as well.