This sample is equal to $ telnet localhost 25
When connected SMTP Server, type like this.
smtp> HELO your.domain [RET]
smtp> MAIL FROM: you@mail.addr [RET]
smtp> RCPT TO: someone@mail.addr [RET]
smtp> DATA [RET]
From: you@mail.addr [RET]
Subject: subject [RET]
Hello, someone.[RET]
.
smtp> QUIT [RET]