How to add DKIM to the IIS

DKIM = DomainKeys Identified Mail

 I am sending emails via C# net 4.0 application. Application is hosted on Windows server 2008 and IIS 7.5

 So far i found that DKIM has to be added to the IIS. How do i do that ?

this is my smtp : http://img28.imageshack.us/img28/7279/smtp.png