Post Office Protocol
The Post Office Protocol (POP) is an Internet standard protocol used by local email software clients to retrieve emails from a remote mail server over a TCP/IP connection.
POP3 provides access to an inbox stored in an email server. It executes the download and deletes operations for messages. Thus, when a POP3 client connects to the mail server, it retrieves all messages from the mailbox. Then it stores them on your local computer and deletes them from the remote server.
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Modern POP3 clients allow you to keep a copy of your messages on the server if you explicitly select this option.