A corporate environment includes Exchange Server 2010. The Exchange Server environment includes two Hub Transport servers, two Client Access servers, and two Mailbox servers on the internal network and two stand-alone Edge Transport servers in the perimeter network. The Mailbox servers are in a database availability group (DAG). You are designing a solution to allow a third-party application to send email messages to both internal users and external users. You have the following requirements:

* Ensure that the third-party application can use domain-based NTLM authentication method for outgoing messages.
* Ensure that if only one server has a hardware failure, all outgoing messages are accepted for delivery.
* Minimize the cost of the solution.

You need to recommend a solution that meets the requirements.

What should you recommend?

A.
Configure DNS round-robin rotation for SMTP connections to the Mailbox servers.

B.
Configure DNS round-robin rotation for SMTP connections to the Edge Transport servers.

C.
Deploy a hardware load balancer for SMTP connections to the Hub Transport servers.

D.
Deploy a hardware load balancer for SMTP connections to the Edge Transport servers.