We like TutaNota at CognitiveMetropolis and think they are worthy of your support. We think this is true not only because they are open source but because unlike other similar services, they take a stand against sharing user information with law enforcement agencies world wide and support connections via Tor. If you truly want to see the difference, read the details in the privacy policy of other providers.
Tutanota is still being under DDoS by unknown adversaries. We are constantly mitigating the attacks. These attacks have been ongoing since middle of August, and while we have immensely improved our DDoS mitigation system since then, we have to keep fighting the attacks to make sure no one can stop you from using encrypted emails.
Link: Continuous DDoS is an attack on our right to privacy.
via tutanota.com