You have a server named Server1 that runs Windows Server 2003 Service Pack 2 （SP2）. Windows Firewall allows the following ports on Server1：  53  110  135  You plan to install a monitoring server on the network.You need to ensure that the monitoring server can use Server1 to relay e-mail messages. You install the SMTP service on Server1. What should you do next？（）

• A、Install SNMP.
• B、Install the POP3 service.
• C、Create an exception for TCP port 21 in Windows Firewall.
• D、Create an exception for TCP port 25 in Windows Firewall.