Asi que aqui se queda, por cierto gracias a Nacho, que me lo paso por mail:

$ telnet smtp.example.com smtp
Trying 192.0.34.72…
Connected to smtp.example.com.
Escape character is ‘^]’.
220 smtp.example.com ESMTP Postfix (Debian/GNU)
HELO smtp.somewhere.net
250 smtp.example.com
MAIL From: alice@somewhere.net
250 Ok
RCPT To: bob@example.com
250 Ok
DATA
354 End data with .
Hello, Bob!
Love, Alice.
.
250 Ok: queued as F169C23068
QUIT
221 Bye