Some HTML emails unreadable (text too small, not zoomable)
Every time I get an email from my twitter account I (barely) cannot read it, because the text is too small, and it is not possible to pinch-zoom in. This is because I cannot set the mail client to only show me plaintext (let alone switch on occasion) and, of course, because the canny people at twitter put a user-scalable=0 and maximum-scale=1.0 in the head of their html e-mails, for whatever reason.
Workaround is forwarding the mail, where I get the plaintext version because thats my default.
I not only heavily encourage #14619 very much, I also encourage the mail client and the browser(-engine) should disregard those pagewide viewport-restrictions altogether in the future as they just don't make sense.