If a company has been contacted because its mail server has been used to spread spam, what is most likely the problem?

A.
The internal mail server has been compromised by an internal hacker.

B.
The mail server in the DMZ has private and public resource records.

C.
The mail server has e-mail relaying enabled and misconfigured.

D.
The mail server has SMTP enabled.

Explanation:
Spammers will identify the mail servers on the Internet that have
relaying enabled and are wide open, meaning the server will forward on any e-mail
messages it receives.