Default transport protocol of POP3 protocol: TCP

Architecture of POP3 protocol: C/S

Access mode of POP3 protocol: offline access

The schematic diagram of POP3 protocol is shown in the following figure:

POP3, whose full name is "post office protocol-Version 3", is "post office protocol-Version 3". Is a member of TCP/IP protocol family, defined by RFC 1939.

This protocol is mainly used to support the remote management of e-mail on the server using the client. The POP3 protocol that provides SSL encryption is called POP3S.

POP protocol supports "offline" mail processing. The specific process is: the mail is sent to the server, and the mail client calls the mail client program to connect to the server and download all unread mail.

This offline access mode is a store-and-forward service, which sends mail from a mail server to a personal terminal machine, usually a PC or MAC. Once the mail is sent to a PC or MAC, the mail on the mail server will be deleted.

Nowadays, most POP3 mail servers can "only download the mail, and the server will not delete it", which is the improved POP3 protocol.

References:

Baidu encyclopedia: pop3