#!/bin/bash  
(sleep 5;
echo "helo [ваш домен]";
sleep 5;
echo "mail from: [от кого письмо - e-mail]";
sleep 5;
echo "rcpt to: [кому письмо - e-mail]";
sleep 5;
echo "data";
sleep 5;
cat /tmp/body.txt;
sleep 5;
echo ".";
sleep 5;
echo "quit";
sleep 5) | telnet [ip или домен] 25

не забываем:
chmod +x [путь/имя].sh