the issues I've always had with it: No support. As in, no one in Google's support organization has any clue about what this app does. No support group discussions as far as I can tell ("Smart Lock" is too generic to really find anything). That's not surprising, because while I've figured out how it works/what it does in my use case, there's really no clear documentation on it - like what it even does, really.

But in the dark world of HTML email, where the motto is "code like it's 1996" because Outlook uses the rendering engine from MS Word and Gmail removes almost everything, every method for making two elements overlap that I can think of is unsuitable due to poor client support

The Gmail Android app that comes pre-installed with most new Android phones contains a feature to access non-Google accounts using POP and IMAP. Unfortunately, emails accessed through this setup lack the embedded style (<style>) support as well as the support for background images.

Great, I can use vw to scale text so it doesn't look puny on a desktop! Perfect... Oh. Huh, now the text is too small to read when viewed on a phone. Okay, well I can just use "max(x,y)" to make sure it doesn't get shrunk beyond a minimum size. Perfect... Oh. Hmm. Looks like "max" isn't supported properly by Chrome. Okay, well guess I'll just use "px" again.