History of E-mail:

Internet based E-mail system was designed by a Computer engineer - Ray Tomlinson in late 1971 while working with ARPANET. Tomlinson used a file transfer protocol to send electronic messages to any computer on the ARPANET network. The first email was sent between two computers that were actually sitting beside each other but connected through ARPANET. The first important email standard was called SMTP, or simple message transfer protocol. SMTP was very simple and is still in use - however, SMTP has a problem - it makes no attempt to find out whether the person claiming to have sent a message is actually the same person. This basic flaw in the protocol was later to be exploited by viruses and worms, and by security frauds and spammers forging identities. Some of these problems are still being addressed. 

In 2004, when Internet standards for email began to mature the POP (or Post Office Protocol) servers began to appear as a standard - before that each server was a little different. POP was an important standard to allow users to develop mail systems that would work with each other.  Now Internet mail is defined by a large number of standards and recommendations by the Internet Engineering Task Force (IETF). However, only a few of the protocols used in Internet mail are full IETF standards. Most of these standards are being used by for people writing Internet mail software.