Say I have hello@example.com and hello@example.net, can I use one unified inbox, and can I use both addresses to send and receive calendar invites?
Moreover, how easy is it to combine my calendars with my work calendar?
I heard it's also not possible to sync contacts with iOS, is that true?
You can also turn on catch all addresses where you'll get all mail sent to anything @yourdomain.com. Very handy to create unique emails for sites I don't want to have my emails I actually use with contacts.
I can't really comment on multiple calendars. I haven't experimented much with that and get all my invites sent to one address.
I think their different plans allow different numbers.
The one what doesn't have any limits other than bandwidth is migadu. But they don't support second fact properly, last I looked.
I migrated from paid proton to fastmail years ago and still happy.
I’ve also used Google Workspace, O365 or whatever MS calls it this week, and Proton as well as self hosting mail in the past.
Usually after using a tool for an extended period of time, there's gonna be some annoyance that you just have to learn to deal with. After five or so years of me using Fastmail, I can't think of a single thing that actually bothers me.