Why smtp.gmail.com returns Unrecognized command?

I've written a winsock clien开发者_Go百科t that connects with smtp.gmail, but after the first EHLO command, every other command would return Unrecognized command. I tryed AUTH, AUTH LOGIN, MAIL...but all return the same thing. Where do I find the commands that works with this server, I think they use SMTP commands differently

They appear to be using an RFC 3207 SMTP/TLS server. Check here for more information: RFC 3207.