You have an Exchange Server 2007 environment. You configure your external e-mail client access to use IMAP4. You configure the external firewall to allow TCP port 993. You need to ensure that your external e-mail clients are able to securely send messages from the Internet by using your Exchange servers. You configure an SSL certificate for secure authenticated SMTP. What should you do next?

A.
Select the Enable Domain Security (Mutual Auth TLS) check box on the default client Receive connector.

B.
Select the Externally Secured (for example, with IPsec) check box on the default client Receive connector.

C.
Configure the external firewall to allow TCP port 25.

D.
Configure the external firewall to allow TCP port 587.