I also use Posteo, one thing to note though is that Posteo doesn’t (and probably won’t any time soon) support custom domains. If that doesn’t bother you, it’s a great choice.
The other alternative I found during my research, which doesn’t have that limitation, is mailbox.org.
I really like Pop!_OS, AFAIK it doesn’t have any telemetry. It’s basically a Ubuntu fork but without the stupid Ubuntu stuff, and they’re currently even working on their own Desktop Environment.