Posteo · Germany
Posteo is built entirely around sustainability and simplicity. It is an independent Berlin-based provider that runs on 100% green energy. Unlike many others, they have no investors and operate only on user fees to remain independent.
The cost is very affordable: just 1€ per month. This includes email, calendar, contacts, and notes. Their model is transparent, you pay for what you need. If you want more storage or extra aliases, you pay a small extra fee, but there are no expensive tiered plans.
Posteo is excellent if you care about the environment and want a service without unnecessary distractions. However, it does not have its own mobile app (you use standard email apps like Outlook or Apple Mail) and it is strictly for personal communication, not heavy teamwork.