Prepare for a somewhat ranty post, but it doesn’t come from a bad place. I honestly want Fastmail to succeed. I’m eager to see more alternatives for email hosting, and clients (and there are scaringly few).
I also acknowledge that some of the problems I bumped into are quite specific to my own setup, which isn’t common. So in some ways, it’s not about you, Fastmail. It’s me. Make your own judgement.
TL;DR – Fastmail is pretty neat, but their support sucks. Their support ticket system sucks even more, and their product is not clear enough to work without support. From my personal experience anyway.