I think he meant Gmail

Thunderbird, gui.

Gemail, Outlook.com/hotmail, thunderbird and outlook all block images, unless whitelisted... Now, there may be other providers/clients that don't, but the above accounts for a significant number of users (if not most western mail users).

Alpine, gui of sorts

K9, gui Android (think it blocks by default, or I turned off auto load when I installed ages ago).

I believe Exchange/O365/Outlook block by default when the senders are outside the organization.

Every mail client I've used, including webmail, has blocked external images by default for at least the last decade.