Racheal is an incident handler working in InceptionTech organization. Recently, numerous employees are complaining about receiving emails from unknown senders. In order to prevent employees against sp

Racheal is an incident handler working in InceptionTech organization. Recently, numerous employees are complaining about receiving emails from unknown senders. In order to prevent employees against spoofing emails and keeping security in mind, Racheal was asked to take appropriate actions in this matter. As a part of her assignment, she needs to analyze the email headers to check the authenticity of received emails. Which of the following protocol/authentication standards she must check in email header to analyze the email authenticity?