Posteo is an email service without advertising, with a focus on sustainability and security.
They offer webmail, calendar (incl. CalDav), contacts (incl. CardDav).
They do not offer to use your own domain and is therefore rather suitable for private users only.
Pricing is very simple. The plan costs 1€/month. If more memory, aliases or additional calendars are needed, these can be purchased separately for additional charges.
Posteo is hosted in different locations around Germany.
Posteo has a big focus on sustainability and provides detailed information about their actions.
They use renewable energy for the servers and the offices.
Read more about the sustainability of the service here