use Telnet to connect to mail server.

simple commands:

HELO <ip-address-of-mail-server> 

The mail server should respond.

http://www.yuki-onna.co.uk/email/smtp.html

telnet: > telnet mx1.example.com smtp
telnet: Trying 192.0.2.2...
telnet: Connected to mx1.example.com.
telnet: Escape character is '^]'.
server: 220 mx1.example.com ESMTP server ready Tue, 20 Jan 2004 22:33:36 +0200
client: HELO client.example.com
server: 250 mx1.example.com
client: MAIL from: <[email protected]>
server: 250 Sender <[email protected]> Ok
client: RCPT to: <[email protected]>
server: 250 Recipient <[email protected]> Ok
client: DATA
server: 354 Ok Send data ending with <CRLF>.<CRLF>
client: From: [email protected]
client: To: [email protected]
client: Subject: Test message
client: 
client: This is a test message.
client: .
server: 250 Message received: [email protected]
client: QUIT
server: 221 mx1.example.com ESMTP server closing connection

CLIENT ONLY

telnet smtp.domain.com 25

HELO smtp.domain.com

MAIL from: <[email protected]>

RCPT to: <[email protected]>

DATA
From: <[email protected]>
To: <[email protected]>
Subject: Test message

This is a test message.
.