I'd like to add https://soverin.net/features here as well. It's similar to Posteo but offers unlimited aliases and more storage. Servers hosted in the Netherlands.
I was a Soverin customer for a year but recently made the switch to Fastmail. I really wanted to like them, but sadly it seems like Soverin is content with their product being in a (barely) beta state. During the year that I used them, there were no improvements to spam filtering (which is abysmal), single sign on (nonexistent), reliability (poor, particularly for caldav) or filtering rules, to name just a few pain points. Their customer service was super responsive, but usually just to tell me that whatever I was asking about (flagging false positives, filtering mail based on an address pattern) wasn't supported.
Soverin, please look at what Fastmail is doing and try to get at least 80% as good. The world needs more fastmails.
Soverin, please look at what Fastmail is doing and try to get at least 80% as good. The world needs more fastmails.