The following examples show how sent and received emails are encrypted in Tutanota. Alice is registered with Tutanota, Bob may be registered with Tutanota or an external recipient and Carol is not registered with Tutanota. In any case all emails (including attachments) are stored encrypted on the Tutanota servers. Independent of the end-to-end encryption, the transport between client and Tutanota servers is secured with SSL and DANE.
Sending and receiving end-to-end encrypted emails
The email is encrypted on Alice' client, stored encrypted on the server and can only be decrypted by Alice or Bob.
Sending non-confidential emails
The email is sent in via SMTP to the recipient. Still, the sent email is encrypted for Alice on the server and then stored.
Receiving non-confidential emails
When the SMTP email is received by the Tutanota server, it is encrypted for Alice and then stored on the server.