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 successfully 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

Explanation:

http://technet.microsoft.com/en-us/library/bb232045.aspx