1) Install Service Pack 1 (optional, but recommended).
2) Open the Exchange Server 2000 System Manager MMC.
3) At the top of the Exchange Organisation (at the very top of the tree in the left hand window), right click, properties and tick Display Routing Groups, and Display Administrative Groups and click OK.
4) Traverse the tree on the left hand window and open up the Administrative Groups, and below that First Administrative Group.
5) Open up Servers, then the name of your exchange server, then Protocols, and then SMTP and then right click on Default SMTP Virtual Server and select properties.
6) In the Access Tab, select Connection Button and check the radio button Only the List Below - add the following addresses using the ADD button.
195.12.4.0 Mask: 255.255.255.0, 195.12.1.0 Mask: 255.255.255.0, 213.83.66.0 Mask: 255.255.255.0 and optionally 127.0.0.1 plus any other relevant IP addresses (for multi-server environments) that you wish to have direct access to this server and click on OK.
7) Click Relay? Button.
8) Select only List below Radio button.
9) Add the following IP addresses.
Add 127.0.0.1, 195.12.4.0 Mask: 255.255.255.0, 195.12.1.0 Mask: 255.255.255.0, 213.83.66.0 Mask: 255.255.255.0 plus any internal IP addresses that you may need to relay through this system (only applicable in multi-server environments).
10) Click OK.
11) Whilst the Default SMTP Virtual Server is still highlighted, right mouse button - STOP (to stop the SMTP Server) and once the service has stopped, right mouse button START to restart the service (alternatively you can use the stop and play toolbar icons at the top of the screen).
12) Voila, server secured.
