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： [e-mail] （[e-mail]）. 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 [e-mail] 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