What is POP3?
POP3 stands for Post Office Protocol version 3 and is a server which stores your email. When an email is sent to you, it is stored on a server (called the POP3 server) until it is downloaded via your email client (Outlook, Netscape Mail, etc.). The email is then downloaded on your server into your mail client or onto your mobile device for you to read and respond to.
This is different to the IMAP email protocol, which stored the email on the server, and allows you to view it through your client, rather than by downloading it directly. POP3 makes it easy for anyone to check their email from any computer in the world, provided they have configured their email program properly to work with the protocol.
POP3 has become increasingly sophisticated so that some administrators can configure the protocol to "store" email on the server for a certain period of time, which would allow an individual to download it as many times as they wished within that given time frame. However, this method is not practical for the vast majority of email recipients. While mail servers can use alternate protocol retrieval programs, such as IMAP, POP3 is extremely common among most mail servers because of its simplicity and high rate of success.