You have an organization that contains Exchange Server 2007 and Exchange Server 2010
Hub Transport servers.
You create a moderated distribution group named Group1.
You assign a user named User1 as the group’s moderator.
User1 reports that some e-mail messages are delivered to the members of Group1 without
his approval.
You need to ensure that all e-mail messages delivered to Group1 are approved by User1.
What should you do?

A.
Modify the expansion server for the group.

B.
Restart the MSExchangeTransport Service.

C.
Force a replication between all domain controllers.

D.
Recreate the group as a dynamic distribution group.

Explanation:

http://www.howexchangeworks.com/2009/12/message-moderation-is-not-working-in.html