Yes! All of our incoming and outgoing gateways as well as our primary SmarterMail system supports STARTTLS as well as SSL. With that though, the sending and receiving server must also support STARTTLS in order to support encrypted mail delivery, while most do, some servers do not. Our systems will always attempt a secured-delivery first then fallback to insecure delivery if not supported.
You can easily test a recipient's server here //email/testTo: (checktls.com) and check your hosted mailbox here //email/testFrom: (checktls.com).
Email protocols such as IMAP, POP and XMPP also offer TLS/SSL encryption as well.