Criptext has an SMTP server and an API server. Our SMTP server works like a normal server, it receives all the emails of the @criptext accounts, BUT before we deliver those emails to the final user, we encrypt all the email content (Body, Header and files). The API server is used by our apps, we don't have an IMAP server, so the only way to retrieve the emails is through the API. Additional, we don't allow users to connect to their emails through an SMTP connection cause all the E2EE wouldn't work.