I'm coding an email for a project and man! it's such a pain. Every other client has it's own implementation and supported rules. Some don't allow even simple properties like background-image while some support most advanced rules like media queries

I haven't done much e-mail templating luckily, but like you said it's a PITA... It would be great if there was some kind of standard though, but that's not going to happen anytime soon

That's something that has been bugging me too. I mean, it's fine if not everything is supported, but if everyone could agree on what is or should be supported then that would make a huge difference. But until then, it's going to be a struggle.