XIMS: Internet Mail Service Reroutes the Message Even Though the "Do Not Reroute" Option Is Selected

When you configure the Microsoft Internet Mail Service for selective IP routing by clicking to select the Host and clients with these IP addresses check box under Routing Restrictions on the Routing tab of the Internet Mail Service Properties page, and add host IP addresses and their subnet mask, the host or client members of this range can route mail, which is the expected behavior. However, if you then configure the Internet Mail service for no routing by clicking to select the Do not reroute incoming SMTP mail check box on the Routing tab of the Internet Mail Service Properties page, mail continues to be routed if it is submitted by the same set of host or client members set during the first configuration.

When you switch back to the Do not reroute incoming SMTP mail option, the values of the routing flags and routing restriction IP addresses are not removed from the registry, which causes the behavior described in the "Symptoms" section.

To work around this problem:

1. In the Exchange Server Administrator program, open the Internet Mail Service Properties page.
2. Click the Routing tab, and enable rerouting by clicking to select the Reroute incoming SMTP mail check box.
3. Click the Routing Restrictions button, and remove all the IP addresses.
4. Click OK, and disable routing again by clicking to select the Do not reroute SMTP mail check box.
5. Restart the Internet Mail Service.

After the address is removed from Routing Restrictions, relaying is prohibited if you test by using Telnet as mentioned in the "More Information" section.

Microsoft has confirmed that this is a problem in Microsoft Exchange Server Version 5.5 Service Pack 3.

Steps to Reproduce the Problem

1. Install Exchange Server 5.5 SP3 with the Internet Mail Service.
2. On the Routing tab of Internet Mail Service Properties page, click to select the Reroute incoming SMTP mail option.
3. On the Routing Restrictions tab, click to select the Hosts and clients with these IP addresses check box. Click Add, and type the IP address of a test client and subnet mask.
4. Apply the changes, and restart the Internet Mail Service.
5. Telnet to the Internet Mail Service from a test client whose IP you used for a restriction in step 3. In the Telnet window, type:
   MAIL FROM:test@test.com
   RCPT TO:anyuser@bogusaddress.com
   
   It should reply with:
   250 OK
   quit
6. Telnet to the Internet Mail Service from another IP address, and attempt to use the same SMTP commands as in step 5. You should get a "relaying prohibited" error.
7. Return to the Internet Mail Service Properties page, click to select the Do not reroute incoming SMTP mail check box, and then cycle the Internet Mail Service.
8. Attempt to use the commands in step 5 again.

Relaying is successful even though the Do not reroute incoming SMTP mail check box is selected.