Instructions for configuring a Smarthost in Exchange:
1) Open the Exchange Management Console
2) Select Edge Transport, if you have a single server select Organization Configuration and Hub Transport
3) Click on the Send Connectors Tab.
4) Now you need to identify which connector is utilized currently for Internet bound email. If you have a simple environment there may only be a single connector configured in which case that is probably the connector you need to modify. If there are multiple connectors we will need to examine the settings on the various connectors to determine which is used for Internet email.
5) Click properties on each connector and look at the Address Space tab
6) Specifically look for a connector that is configured with an Address Space of * SMTP which indicates this is responsible for * (ALL) email other than those with internal names spaces such as your organizations email.
7) Once you have determined the Connector that needs to be modified open properties on that connector and click on the Network tab
8) Change the radio button to "Route mail through the following smart hosts"
9) If there were any previous Smart Host names please remove those from the configuration
10) Click the Add button and add a FQDN or IP address of your SpamTitan server and click Ok
11) Ensure that the Smart Host authentication is set to "None". if not then click the Change button and clear the settings there
12 Click Apply/Ok and exit the properties for the send connector
Also, before you do any of this, please make that the SpamTitan has been configured to accept mail from your Exchange Server. This in done in System Setup > Mail Relay > Trusted Networks