Russell, Please don't take my comments as a knock on Mailgun. You guys rock. It was more the frustration with the idea that 1) encryption is optional for cert

Russell, Please don't take my comments as a knock on Mailgun. You guys rock. It was more the frustration with the idea that 1) encryption is optional for certain network protocols, and that 2) you upgrade a plaintext connection to a secure connection. This simply fails in practice, and we have seen this time and again with HTTP/HTTPS. 1) is changing, which is good. 2) is something people keep pushing for because it should work. Afterall you can configure your server to require a STARTTLS, and have all your client's configured to always use STARTTLS and abort out if it doesn't become secure. Stop that. You are already making this to complicated. Crypto is hard enough as is. (See lower comment re: Comcast and STARTTLS). Ignoring the fact that you are mixing Layer 5/6 concepts into your Layer 7 application prototol, you are creating an insecure-by-default system. Its plaintext, unless you do these things. Stop that. You are doing it backwards. Make it a separate port, and SSL/TLS happens before the application protocol is even accessed. "Is this connection secure" and tracking state and transition into/out of that is not the job of an application protocol. Make this simple and boolean.