How to remedy Exchange 5.5 IMS default open relay behavior

Introduction:
The following are basic steps to ensure that your registered domains and IP addresses do not get added to MAPS or any other mail abuse databases.  This procedure should be the first step in protecting your server from being brought to it's knees by SPAMMERS looking for a free server to distribute unsolicited messages to bulk recipients.  Unfortunately, by default, Exchange 5.5 configures it's IMS as an SMTP open relay.  This basically means that anyone inside, or outside, can use your IMS to deliver messages virtually, anywhere they'd like to.

Procedure to correct this situation:

1. Connect the Exchange Administrator program to an Exchange server which is running the Internet Mail Service (IMS).
    

2. Navigate to the connections container, which is a sub-container, under site configuration.
    

3. Open the properties page of your IMS object.
    

4. Click on the routing tab, of the properties page.
    

5. Click on the 'routing restrictions' button.
    

6. Check the box titled "Hosts and Clients connecting to these IP addresses".  If you need to have any internal machines use this box to relay mail, add the ip addresses as either individual entries, or a single entry which covers a range of addresses.  For a single address, be sure to specify a subnet mask of 255.255.255.255.  To cover a subnet such as 10.x.x.x, use a single entry of 10.0.0.0 with a mask of 255.0.0.0.
    

7. Restart you IMS service for the change to take effect.
    

8. Test using an SMTP client such as Outlook Express, or telnet on port 25.