I recently added a new anti-spam and anti-virus solution to my network. After reviewing my installation options I installed the applications on a mail relay to prevent any performance loss on my already under powered mail server. I decided to use a Windows 2003 server to act as the smarthost for my Exchange server and filter spam and viruses before it ever reaches my Exchange server.

After installing the SMTP Service on the smarthost we need to set it up to relay incoming messages for your domain(s). Open up the IIS Manager and drill down until you get to the Default SMTP Virtual Server and expand it. Under this heading you should see Domains, right click this and select New --> Domain.

Follow the wizard and create a new Remote domain,

.... and enter the DNS name of your domain.

Repeat this for all domains that you need to relay inbound messages for. Now we need to configure the domain to relay. Right-click the domain you just added and select Properties. Here we need to check the box next to "Allow the Incoming Mail to be Relayed to this Domain" and enter the IP address of the destination mail server in brackets. i.e. [192.168.1.1]

The brackets will distinguish the IP address as such instead of treating it as a DNS name. If you wish you could enter the DNS name of the server, without brackets, but this could put an unnecessary strain on your DNS infrastructure. Next step is to allow only your mail server(s) to relay outbound messages. Not performing this step will leave you with an open relay and it WILL be used by spammers to send messages. Hop back into the properties of the Default SMTP Virtual Server and click the Access tab, then click the Relay button. Here we will enter the IP address(es) of the mail server(s) you wish to allow to relay outbound mail. First select the "Only this list" radio button and the add the IP address(es). You can also allow a range of IP addresses with and IP/Subnet combo i.e 192.168.0.0 255.255.255.0 would allow 192.168.0.1 to 192.168.0.254 to relay outbound mail. You can also specify a domain name but again this puts unnecessary strain on your DNS infrastructure.

Lastly we need to restart the SMTP service on the smarthost and configure the email server to use the smarthost. In Exchange this is done on the SMTP Virtual Server Properties, Delivery tab, press the Advanced button and enter the IP address, in brackets, under the Smarthost heading. Restart the SMTP service and email will now send out through the smarthost.