An example of POP3 is how email is stored on a server until the recipient downloads and reads the email.
POP3 - Computer Definition
An IETF standard (RFC 2449) for a store-and-forward service used by a client to retrieve e-mail from a remote server over an IP network. Prior to accessing a mailbox at the remote server and downloading all mail to the client, the user can elect either to delete downloaded mail from the server or to leave a copy of each on the server. After downloading mail, the user can disconnect from the remote server and work with the mail offline. POP3 is used only when downloading mail from the mailbox.When uploading mail, client access is to a server running Simple Mail Transfer Protocol (SMTP), which simply forwards mail after looking up the proper IP addresses on a Domain Name Server (DNS) server.While POP3 is widely implemented, the more recent Internet Message Access Protocol (IMAP) offers certain advantages. See also client, DNS, e-mail, IETF, IMAP, IP, RFC, server, and SMTP.
(Post Office Protocol 3) A programming interface (API) from the IETF that enables a user's e-mail program to access the mail server (RFC 1939 standard). E-mail clients such as Outlook, Mail, Eudora and Thunderbird are typically configured to retrieve mail either via POP3 or IMAP4, the other popular standard. POP3 is a simple system with limited selectivity. Incoming messages and attachments are downloaded when users check their mail, and POP is typically configured to delete the messages on the server after downloading. If the user opts to not delete them, the messages will download again the next time mail is checked. See IMAP4, e-mail interfaces, SMTP and messaging system.