I just migrated away from Tuta after trying the service for a year. I like it well enough, but it presented too many frustrations to be a service to pay for.

1. While they have labels (yay!) their inbox rules cannot apply labels so you are stuck manually tagging everything (boo!) - and the UI for manually tagging could use improvement.
2. Mobile (Android) notifications stop working frequently.
3. While they integrate their contacts in to the Android contact list, they refuse to integrate their calendar with the Android system calendar - meaning I cannot pull a consolidated list of calendar events in to my launcher, and am stuck using their calendar application (which could use a lot of improvement).
4. If you set a calendar event reminder, and then change the time of the event, the reminder will go off at the original event time (or 15/30 minutes before, whatever you set it to).
5. Long refreshes when loading the inbox. Navigating back to the application often has the server disconnected, then you have to wait a spell for it to reconnect so you can carry on.

After searching around and checking purelymail, infomaniak, mailbox.org, mxroute, migadu, zoho, etc. I landed on fastmail (with my own domain) predominantly because of their implementation of labels (super slick). Their mobile app and desktop applications are also very slick. Contacts/calendar sync in to the Android System is done through DavX, but I also have it syncing to my Nextcloud instance. It's a more expensive solution than the others, but labels (tags/categories) are such an important part of my workflow that there aren't a lot of options unless I wanted to go back to M365/Google Workspace.

If I was to give up labels, I'd probably go with infomaniak or mailbox.org. Both of their offerings were slick and the price was right.