You need to ensure that all email messages delivered to Group1 are approved by User1.

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 email messages are delivered to the members of Group1 without his approval.

You need to ensure that all email messages delivered to Group1 are approved by User1.

What should you do?

A.
Recreate the group as a dynamic distribution group.

B.
Restart the MSExchangeTransport Service.

C.
Modify the expansion server for the group.

D.
Force a replication between all domain controllers.

Explanation:
Reference:

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