You deploy a new Exchange Server 2010 organization.You send a test message to an external recipient and immediately receive the following nondelivery report （NDR）： Delivery has failed to these recipients or groups： User1@contoso.com （user1@contoso.com）. The recipient’s e-mail system isn’t accepting messages now.Please try resending this message later or contact the recipient directly.± You verify that you can succesfully send an e-mail message to User1@contoso.com from an external e-mail system.You need to ensure that you can send e-mails to external recipients from within the Exchange organization. What should you create？（）

• A、a Send connector
• B、an accepted domain
• C、an MX record
• D、an SMTP site link