Your network consists of a single Active Directory domain and 10 Active Directory sites. contains an Exchange Server 5.5 contains an Exchange Server 2003 server and UNIX-based SMTP server.
You configure the UNIX server in each site to relay outgoing e-mail messages through the Exchange Server 2003 servers.
E-mail delivery from the UNIX-based SMTP servers to the Internet fails.
You need to enable the UNIX servers to relay SMTP messages through the Exchange Server 2003 servers.
What should you do on each Exchange Server 2003 server?

A.
Add a SMTP virtual server that allows anonymous SMTP connections.

B.
Create a new SMTP virtual server and enable the local Guest user account.

C.
Create an SMTP connector and configure the local UNIX server as a smart host.

D.
Configure the default SMTP virtual server to relay SMTP messages from the IP address of the local UNIX