Used FastMail as part of my big DeGoogle initiative last winter. Very happy with it. However, one of the main considerations of Fastmail vs. other providers is that the domains they used are 'Visa-free' in terms of spam catchment - everything gets through!

But some have noted that FM is an Australian service with some interesting issues around privacy and five-eyes surveillance.

For me, in the end, I had to pay that price (as well as the sensible prices of the service itself), because I really needed my business mails to arrive in people's inboxes.