Dynamic Recipient Verification (DRV) is the easiest form of Recipient Verification to use and manage. First you have to enable Recipient Filtering on your mail server, see the links below for guides for commonly used mail server software:
http://technet.microsoft.com/en-us/library/aa998898%28EXCHG.80%29.aspx to configure Exchange 2007
If you are using a default standalone (no Edge Transport Server) installation of 2010 the Anti-Spam functionality is not installed. Therefore you need to follow this article:
http://technet.microsoft.com/en-us/library/bb201691.aspx to enable it.
To configure Recipient Filtering for Exchange 2010 see:
To configure recipient verification in Postfix see:
Once Recipient Filtering is enabled log on to the SpamTitan web interface. Browse to System Setup->Mail Relay->Domains. Edit a domain and select "Dynamic Verification" and enter your mail server IP as the Verification Server.
This will allow SpamTitan to verify the recipient addresses of all incoming mail. Any mail addresses to invalid addresses will be dropped. This will aid the spam block rate and keep your daily license usage count accurate.