POP3 is the third version of the Post Office Protocol, one of the popular standard protocols that servers utilize in handling email messages. As of 2014, It is commonly used by popular email clients and webmail service providers, including Gmail and Yahoo Mail.
With POP3, incoming email messages remain stored in remote servers until users log in to check their email accounts. At that point, the messages are downloaded to the users' computers and the server copies are deleted. Its simple mechanism in handling incoming messages makes it a viable choice for personal email accounts. Business email accounts, on the other hand, often use more complex protocols, such as the IMAP or Internet Message Access Protocol.