POP3 is the protocol used to retrieve email from a server in its version 3 form.
POP3 stands for Post Office Protocol version 3. It is an application-layer Internet standard designed for a mail client to contact a server, list messages, download them, and optionally delete them. POP3 became popular when many users connected through slow or temporary dial-up links: messages could be downloaded and read offline.
Its design differs from IMAP. A traditional POP3 workflow treats the server mailbox as a source for downloading mail, while the client keeps the main working copies locally. Modern POP3 clients can often leave messages on the server, but POP3 still offers much less server-side organization and synchronization than IMAP. SMTP is commonly involved in sending mail, not retrieving it, while NNTP is associated with network news. POP3 is commonly secured with TLS, including connections using port 995 or STARTTLS on port 110.