Sending mail from telnet session

This procedure is commonly used to troubleshoot SMTP hosts. In combination with a nslookup query for MX records for a domain (listed after this) you can successfully figure out if a given domain can receive internet email successfully.

1) Open a telnet session to a SMTP - let's say foo.mydomain.com - or an IP address
telnet foo.mydomain.com 25
What you get back:
220 foo.mydomain.com Microsoft ESMTP MAIL Service, Version: 6.0.3790.1289 ready at Wed, 19 Oct 2005 10:27:34 -0700

2) Now you can say where you're sending mail from using HELO
helo foo2.somedomain.com
250 foo.mydomain.com Hello [65.239.32.15]

3) Provide sender's address
MAIL FROM:[email protected]
250 2.1.0 [email protected] OK

4) Provide recipient's address
rcpt to:[email protected]
250 2.1.5 [email protected]

5) To start message content, issue the DATA command
DATA
354 Please start mail input.

6) Enter the Subject
Subject: This is a test


7) Type in the body
This is a test from [email protected]

8) To end the message, enter a dot in a new line followed by Enter
.

250 Mail queued for delivery.

10) Close the connection
quit
221 Closing connection. Good bye.

How to determine the mail exchanger (MX) for a domain

You can use the following procedure to determine the mail servers designated as "mail exchangers" for a domain. This is done by inserting a MX record for those servers in the DNS. Best practice for MX records is to point them to A records. A records are simple hostname to IP address mappings.
Pointing MX records to CNAME records may result in performance issues.

From a command prompt, type:
nslookup -querytype=MX somedomain.com

This should produce output similar to the following:
Server: ns1.mydomain.com
Address: 192.168.1.10

Non-authoritative answer:
somedomain.com MX preference = 10, mail exchanger = mx1.somedomain.com
somedomain.com MX preference = 20, mail exchanger = mx2.somedomain.com
mx1.somedomain.com internet address = x.x.x.x
mx2.somedomain.com internet address = x.x.x.x