At this point, the battle for only sending plaintext has been decisively lost. What I'd much rather fight for, now: please always send a valid text/plain part,

At this point, the battle for only sending plaintext has been decisively lost. What I'd much rather fight for, now: please always send a valid text/plain part, that includes the full content, including things like the verification code for email verification, or the URLs for anything you expect the user to follow. Some services send emails that have a text/plain part, but the text/plain part has things like "click here to ..." and the URL to click on is not present.