You are a systems administrator responsible for configuring a Windows Server 2008 SMTP server. Yourorganization is currently using the default SMTP virtual server for sending order notifications from a single Web application called ContosoOrderManagement. Recently， you have noticed that a largenumber of messages have been sent to the SMTP virtual server from other computers and users. Which two methods can you use to prevent unauthorized access to the SMTP server？（）

A. Enable Basic Authentication.
B. Configure a smart host for use by the SMTP virtual server.
C. Add Connection Control entries to limit which IP addresses can use the SMTP server.
D. Modify settings on the Security tab of the properties of the SMTP virtual server.