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(following campaignmonitor.com/css/b).
With every other change I make, I have to test in a dozen clients and make sure it looks fine.
Why is there so much variation in email style implementation amongst different clients?