Fastmail is an excellent company with an amazing product. The web UI really is insanely fast. And with keyboard shortcuts you can be super productive. They’re also pushing new standards (JMAP) and seem committed to privacy and best practice etc. Really one of my favourite tech companies. Not an employee just a happy customer!
I've got around 10 domains there, each of which have up to 4 addresses. Emails arrive filtered into separate folders in the same account, so I get all that whilst only paying for a single account (they'll even host static sites for all those domains, though I currently use Netlify).
Always performant, excellent web UI for mail, contacts, calendar, and (optionally but included) DNS, and if they have occasional blips I have to say I've never noticed.
Far superior to GMail, which these days seems stale and slow (and possibly only gets away with it because it is ubiquitous enough to set the level of people's expectations).