Mail Relay Test

An outside individual who uses your mail server to deliver email using a false email address is considered relaying mail via your server. A mail server that allows relaying is usually considered to be setup incorrectly and is frequently abused by spammers. These spammers find and use unsecured mail servers to send out unsolicited commercial email.

Tracking down a spammer who uses mail servers open to relaying is difficult. This is because the email appears to be coming from your server, rather than from the original sender. Such spam being delivered by your mail server can give your company a bad reputation.

Email Relay Test

How do you check your server for relaying?  Easy, just use a computer outside of your organization and type the commands included in the tables below – you’ll want to do this from a command prompt.

In the following examples, mail.example.com is the mail server you are checking, sender@example.com  is a valid email account at mail.example.com (or a fake email address – try both), and youremail@outsideaddress.com is the email account you want this message to go to.

The parts you type are show in the table blow and replies from the server are shown to the right. This is an example of a mail server that does NOTallow relaying.

You type this text	Server should respond with this
TELNET mail.example.com 25	Trying 10.10.10.1. Connected to mail.example.com. Escape character is ‘^]’. 220 mail.example.com
HELO mail.example	250 OK
MAIL FROM:<sender@example.com>	250 OK – Mail from <sender@example.com>
RCPT TO:<youremail@outsideaddress.com>	550 Relaying is prohibited
QUIT	221 Closing connect, good bye

This is an example of a mail server that DOES allow relaying.

You type this text	Server should respond with this
TELNET mail.example.com 25	Trying 10.10.10.1. Connected to mail.example.com. Escape character is ‘^]’. 220 mail.example.com
HELO mail.example	250 OK
MAIL FROM:<sender@example.com>	250 OK – Mail from <sender@example.com>
RCPT TO:<youremail@outsideaddress.com>	250 OK
DATA	354 End data with <CR><LF><CR><LF>
From: sender@example.com To: youremail@outsideaddress.com Subject: Relay test This is a relay test and only a test. (type  <CR><LF>.<CR><LF> or [enter].[enter] to end data)	250 OK: Queued as T22122A5
QUIT	221 Closing connect, good bye

 

Preventing message relaying with MS Exchange

Before you start, check which version you are running – you must be running Microsoft Exchange Server 5.5 or greater, then follow these 7 steps.

1. Go to the Internet Mail Service Properties dialog box in Microsoft Exchange
2. Select the Routing tab at the top.
3. Select the option Reroute incoming SMTP mail (required for POP3/IMAP4 support).
4. Reroute incoming SMTP mail.
5. For each domain you host, you need an entry in the Routing section.
6. Click the Routing Restrictions button.
7. Make sure Hosts and clients with these IP addresses is checked. Leave the list of IP addresses blank.

Microsoft knowledge base has more information at http://support.microsoft.com/?kbid=304897>