Telnet to your mailserver
telnet mail.domain.com 25
EHLO domain.com
MAIL FROM:<sender@domain.com>
RCPT TO:<recipient@domain.com>
DATA
Subject: This is a subject line
Press Enter twice; a blank line is needed between the Subject field and the message body.
Type the rest of your message, then press Enter.
To finish the message, type a period ( . ) and press Enter
QUIT