PROBLEM:
Configure "Dynamic Recipient Verification" for SpamTitan.
How to Enable "Dynamic Recipient Verification" for Exchange 2007 / 2010 / 2013?
SOLUTIONS:
SPAMTITAN (Part 1)
1.) In the SpamTitan Dashboard.
2.) Go to, System Setup > Mail Rely > example.com and click on edit.
3.) Under "Recipient Verification" choose "Dynamic Recipient Verification".
4.) Save.
EXCHANGE (Part 2)
5.) In the Microsoft Exchange Management Console.
6.) Go to, Organization Configuration > Hub Transport.
7.) Enable "Recipient Filtering".
(http://adventech.net/downloads/techfortechs/HubTransport-Recipient_Filtering.PNG)