You are an email administrator for a large company. Recently a series of emails were sent from a user's email account that the user claims not to have sent. How should you proceed?
Disable the user account, reset the password and run an anti-malware scan on the user's PC
Tighten firewall restrictions to block the SMTP port (25)
Ask the user to please stop sending the emails
Disable the email and provide a new account to the user