XFOR: Restricting Routing in the Internet Mail Service

The Exchange Server Internet Mail Service (IMS) allows you to configure the server to allow mail relaying. When you enable the Mail relaying in the IMS's 'Routing' property page, all mail will be routed without restrictions. Exchange Server 5.5 Service Pack 1 allows the administrator to impose restrictions on routing.

To enable these restrictions on routing functionality, follow these steps:

1. Install Exchange Server 5.5 Server Pack 1 (or later).
2. Open the properties on the Exchange Server Internet Mail Service and select the Routing page. After the SP1 installation, this page will have an additional button called <Routing Restrictions...>.
3. Click Routing Restrictions to bring up a dialog box with additional Restrictions.

Exchange Server 5.5 Service Pack 1 adds "Routing Restrictions" to the Internet Mail Service. This allows the administrator to specify who can relay mail off of your Exchange Server computer.

The following Restrictions have been added:

Specify the hosts and clients that can route mail when the following conditions have been met.

• Hosts and clients that successfully authenticate:
  
  Messages sent from hosts and clients with valid logon information are relayed.
• Hosts and clients with these IP addresses:
  
  Messages sent from host whose IP addresses and subnet mask fall within the range to be allowed to relay.
  
  To only allow a single host or client, enter in the format, IP=>full IP address of client< (i.e 1.1.1.1), MASK=255.255.255.255
  
  To allow a range of IP address to relay, enter in the format, IP=>scope to allow< (i.e 1.1.1.0>, MASK=255.255.255.0. This will allow the address range of 1.1.1.1 - 1.1.1.254 to relay.
• Hosts and clients connecting to these internal addresses
  
  Messages sent by hosts and clients that connect to the specified IP address on the Microsoft Exchange Server computer are relayed. This allows multihomed servers to restrict message relay based on the IP address to which the client connects. If you select this option, you must disable IP forwarding on the Networking property pages in Control Panel.

Specify the hosts and clients that can NEVER route mail.

• Messages sent from the specified IP addresses and subnet mask are NOT relayed.