Encrypt with TLS
To transmit secured, authenticated, and verified communications between two or more systems, Twilio Email uses the symmetric cryptography of the Transport Layer Security (TLS).
Four RFCs define TLS:
When attempting to deliver email, Twilio Email opportunistically tries outbound TLS v1.1 or later.
If your recipient's email server accepts an inbound connection using TLS v1.1 or later, Twilio Email encrypts then delivers the email message between systems. If the server doesn't support TLS, Twilio delivers the message unencrypted.