Sending mail using smtp commands via telnet

I'm working on testing that mail is delivered properly from outside our network, through our various virus and spam filters and to the appropriate email server. I would like to telnet into one of our mail gateways and send a message from there destined to a new internal server. I know how to telnet into the mail server, but I'm not finding the appropriate commands to actually send a message once I'm connected. Can anyone point me in the right direction. My googling skills have failed me on this one since I can't seem to hit the magic phrase necessary to find a resource on this topic. Any help, pointers, references greatly appreciate. Thanks. Rob