A network administrator is tasked with blocking unwanted spam is being relayed by an internal email server. Which of the following is the FIRST step in preventing spam that is originating from bots on the network?
A. Closing off port 25 on the firewall
B. Closing off port 53 on the firewall
C. Turning off the SMTP service on the email server
D. Turning off the IMAP service on the email server
