History

• Although the first email message across a network was sent in 1971, Internet standards related to email storage did not appear until the mid 1980s. These protocols ultimately evolved into the Post Office Protocol-Version 3, or POP3 server, adopted as an Internet standard in May 1996. In keeping with the Internet Engineering Task Force's goal "to make the Internet work better," the standard continues to evolve through regular proposals to enhance security and add functionality to POP3.
  
  

What It Does

• Email from the POP3 server is delivered to the client's inbox.Email LCD display image by Alex Yeung from Fotolia.com
  
  Interacting with the POP3 server is the "checking messages" portion of a user's email experience. In other words, email messages from around the Internet are collected and transmitted by other services such as Simple Mail Transfer Protocol (SMTP) and stored on the POP3 server--called the maildrop--until the recipient accesses them. By running his preferred email application--the email client--that user downloads messages from the POP3 server onto his computer.
  
  

How It Works

• An Internet server running the POP3 service accepts network connections from email clients on a particular network "channel" known as TCP port 110. The server responds with a greeting and a request for authentication. The client generally sends back a username and password combination; if these match the POP3 server's records, the process of transferring email messages from the server to the client computer begins.
  
  

Caution

• It is important to note that a POP3 email client is often set to delete email from the server by default. As a result, once the client downloads the messages, they are gone from the server. This means that users who check email from multiple computers will not have one single location for all email. It also means that without a regular data backup plan, a computer crash could result in all email being lost.
  
  

Alternatives

• Other methods of reading email include Internet Message Access Protocol (IMAP) or through web-based access. An IMAP server works similarly to a POP3 server by delivering messages to an email client, but is a better option for users who check email on multiple computers. Many email providers offer access to messages using only a web browser. This eliminates the need for any special email client and allows users to access email from any Internet capable device with a web browser. Both of these solutions offer the benefit of external data backup, but both impose limits on the overall size of a user's mailbox. A user connecting to a POP3 server retains complete control over how many messages she wishes to keep and how much disk space her mailbox consumes.