I'm an extreme niche, so I recognize that an email client that intends to be used by the general population would need it, but why would I even want to see HTML emails? Those are 105% of the time just marketing bullshit. Emails are either in plaintext with friends/families/clients/people or have a single link that I can copy/paste to verify an account on a website. As it stands, I never download images in my emails anyway. A few sites have tried serving the account verification code as an image and I just won't validate my account if that's the case.

Designed emails using HTML are used by marketing teams - not by people. I don't care to read emails from marketing teams "as intended to be viewed". Show me the email and let me read an email that's just a bunch of plaintext markup.