I am a posteo [1] subscriber. Superior set of features [2] (privacy, security, encryption), runs on green power, no ads / tracking, groups in address book, nice staff -- for 1€ per month. Also supports mandatory TLS transfer (or doesn't send the email), if wanted. Couldn't be happier since ~5yrs!

[1] https://posteo.de/en [2] https://posteo.de/en/site/features#featuresprivacy