You have an Exchange organization. All servers in the organization have Exchange Server
2010 Service Pack 1 (SP1) installed.
You need to prevent external organizations that do not have sender policy framework (SPF)
records from sending e-mail messages to the organization.
What should you configure?

A.
an IP block list provider

B.
sender reputation

C.
sender filtering

D.
sender ID filtering

Explanation:
http://technet.microsoft.com/en-us/library/aa996295.aspx