To send an e-mail to a mail-server use the following commands:
Telnet <hostname_of_mailserver> 25
MAIL FROM: <yourname>@domainname.tld
RCPT TO: <firstname.lastname@example.org>
<enter your message>
The e-mail server should send the message out. Normally (to block relaying) the server will only send e-mails from your own domain!