Email spoofing refers to:

• A. The forgery of an email header so that the message appears to have originated from someone or somewhere other than the actual source
• B. The criminal act of sending an illegitimate email, falsely claiming to be from a legitimate site in an attempt to acquire the user's personal or account information
• C. Sending huge volumes of email to an address in an attempt to overflow the mailbox or overwhelm the server where the email address Is hosted to cause a denial-of-service attack
• D. A sudden spike of "Reply All" messages on an email distribution list, caused by one misdirected message

Answer: (A)

Email spoofing is the forgery of an email header so that the message appears to originate from someone or somewhere other than the actual source. This happens because the email protocol (SMTP) doesn’t reliably verify who sent a message, allowing attackers to modify the header information or use forged addresses to misrepresent the sender. The goal is to deceive the recipient, often to facilitate phishing or social engineering, by making the email look as if it came from a trusted source.

The other descriptions move away from the mechanism itself: one describes sending illegitimate messages that pretend to be from a legitimate site to steal information, which is phishing but not the header-forgery mechanism itself; another describes overloading a mailbox or server to cause a denial of service; and the last describes a mass reply scenario due to a misdirected message.