Using expect to drive netcat - Simply piping the required sequence of commands into netcat is unlikely to work because the SMTP commands and responses would not be properly interleaved. If you want to use the method above from a script then you will need to make use of a program such as expect. Here is an example:

expech.sh

#!/usr/bin/expect

set timeout 30
proc abort {} { exit 2 }

spawn nc -C mail.example.org 25
expect default abort "220 "
send "HELO example.com\r"
expect default abort "\n250 "
send "MAIL FROM:bar@example.org\r"
expect default abort "\n250 "
send "RCPT TO:foo@example.org\r"
expect default abort "\n250 "
send "DATA\r"
expect default abort "\n354 "
send "From: bar@example.org\r"
send "To: foo@example.com\r"
send "Subject: Test\r"
send "Date: Thu, 20 Dec 2012 12:00:00 +0000\r"
send "\r"
send "Testing\r"
send ".\r"
expect default abort "\n250 "
send "QUIT\r"