Thanks - looks nice, especially as it's native. I'm using Fluid (fluidapp.com) to wrap Fastmail which also gives the ability to show notifications, show dock badge and handle mailto:. It also allows the use of custom CSS or JS which I find indispensable (see <a href="https://github.com/mdbraber/fastmail-customized" rel="nofollow">https://github.com/mdbraber/fastmail-customized</a>). For shortcuts I use Keyboard Maestro w/ specific JS commands or URL triggers.
This is a small project that I made mostly for my own use. I did learn about Fastmail through HN, so maybe someone else here has use for something like this!