You can install any email client available on ubuntu, e.g. thunderbird. No need to use Elementary's stock apps.

OP here - Yes and no. Mail can now cope much better with some HTML email, but there still isn't an obvious way to add a signature (I allude to that in the post).

Why would you want an HTML signature?

Some companies will require you to use a signature with an image and particular formatting. Also, tackiness is in the eye of the beholder.

It's a common use case that's why.

Mail used to use webkitgtk (the old api), but has been since ported to use webkit2gtk (the new, multi-process api), you might wanna give it a second look.

EDIT: I stand corrected. This has not happened yet. I confused this with some other changes.