There are two ways a message can be transmitted over an encrypted communication channel via SMTP. Here at SocketLabs we support both methods on our inbound SMTP gateway, smtp.socketlabs.com.
The first method of achieving secure message transmission is with an SMTP protocol command called STARTTLS. This is commonly referred to as explicit SSL/TLS. In this case an unencrypted connection is established and then the client attempts to determine if the server supports upgrading the current connection into an encrypted session. The connection upgrade begins with the client issuing a STARTTLS SMTP command. SocketLabs currently supports the STARTTLS protocol command on the inbound gateway smtp.socketlabs.com. It can be used over ports 25, 2525, and 587.
Secondly, a secure connection using SSL/TLS can be established upfront in the connection attempt and then all resulting SMTP communications will be secure. This is commonly referred to as implicit SSL/TLS. This is a less commonly employed means of in transit message encryption. SocketLabs' primary inbound SMTP gateway smtp.socketlabs.com currently supports this method of encryption over port 465. It is important to note that insecure connection attempts to port 465 are not accepted. If you are unable to connect to our gateway on port 465, please check your SSL/TLS encryption settings and ensure that you are not attempting to use STARTTLS.
We do not support unencrypted HTTP connections to our Injection API.
All messages transmitted to SocketLabs via the Injection API are done so over an encrypted HTTP connection.
It is important to note that the secure injection of messages to our inbound SMTP gateway or Injection API does not impact whether or not a message is delivered by our platform securely to the end recipient. To customize your server's secure delivery options, please see Secure Message Delivery (SSL/TLS) Options. For more information and secure message delivery see our blog article on the topic: http://www.socketlabs.com/blog/securing-and-protecting-the-privacy-of-your-email-with-ssl-tls/
All other questions about secure messages injection and secure message delivery can be answered by the SocketLabs On-Demand Support Team.