A penetration tester has gained access to the Chief Executive Officer's (CEO's) internal, corporate email. The next objective is to gain access to the network. Which of the following methods will MOST likely work?

A. Try to obtain the private key used for S/MIME from the CEO's account.
B. Send an email from the CEO's account, requesting a new account.
C. Move laterally from the mail server to the domain controller.
D. Attempt to escalate privileges on the mail server to gain root access.