I know there is a lot of discussion on if people are still planning to inline their code after Gmail announced support for styles in the header. From what I have seen first hand though, they have only rolled that out for actual gmail addresses and not others using the Gmail App. For example, I use an Office 365 hosted Exchange Server address in the Gmail app on Android. No styles in the header work for me. Hopefully this will change, but since many clients almost certainly do the same thing I do, that means inlining apparently is still needed. I'm very sad about that. :-(