Internet was invented by people who were good at programming, and people keep optimizing it for different purposes. So Internet has been growing organically. Internet can achieve many things but has advantages and disadvantages. The email system was designed by graduate students and researchers who know and trust each other. Using email needs trust between the senders and the receivers as the authentication process was not originally built in this system. Email authentication is a technical solution to proving that an email is not forged. In other words, it provides a way to verify that an email comes from who it claims to be from. Email authentication is most often used to block harmful or fraudulent uses of email such as phishing and spam. In practice, we use the term “email authentication” to refer to technical standards that make this verification possible. Initially, the email system didn't consider security because there was no suspicion between them at that time.