You work as the enterprise exchange administrator at Xxx .Xxx is using Microsoft Exchange Server 2010 as their messaging solution.The Xxx employees at Xxx use Outlook Web App to access their mailboxes.You receive a complaint from a Xxx employee named Mia Hamm that her mailbox is unavailable.What actions must you take to resolve this problem？（）

• A、You must change the WEB Outlook Provider.
• B、You must change Mia Hamm’s mailbox features.
• C、You must change the EXPR Outlook Provider.
• D、You must change the DNS forwarding.