@Andres @chesheer TIL there are more than one Posteo. He is referring to https://posteo.de/de, a German email provider.

@chesheer one more vote for Posteo. Here in Germany, they have become quite mainstream and are used by many people not in IT in my bubble. It works reliably on any device, has fast service response times, and has some goodies like S/MIME certificates for a few euros per month. And it does what you want: email without any extras. I am pleased with them.