After running my own server for a few years, I got tired of the maintenance. I used ProtonMail for a while, and I didn't mind using their app on my phone and the Bridge on my computer, but my parents kept forgetting to check and update it so Thunderbird would lose connectivity once in a while.

I have since migrated to Infomaniak. It's based in Switzerland as well, you can use your own domain and it's cheap (€1.50 per month for 5 addresses with unlimited storage). I haven't tried their smartphone app (I use the one from Apple on my iPhone), but I've heard good things about it.