Post Office Protocol

Essay by zzzaaaqqq December 2004

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The Post Office Protocol (POP) was first issued on October 1984. The protocol suggests a simple method for workstations to access mail from a mailbox server.

The protocol is dependent upon TCP (Transfer Control Protocol) and assumes that mail is posted by SMTP.

POP in more detail, is a way for a server machine to store and serve mail for various client machines that are not connected to the Internet 24 hours a day. This makes it like an electronic Post Office Box, where your email is held in the POP server until you login and retrieve it.

For example, if somebody sends you e-mail it usually cannot be delivered directly to your computer unless it is permanently connected to the Internet and has its own mail delivery system. The messages have to be stored somewhere. An Internet Service Provider is on-line 24 hours on 7 days of the week and can do that job.

This is where the message will stay until either you retrieve it or the Internet Service Provider administrator (ISP) finds a pile of large storage files from messages. The ISP then deletes them because you have gone past your limit of space available for incoming messages and cannot receive any more.

The advantages of POP is that you can read your-e-mail from anywhere on the Internet that you can run a POP client, without having to dial-up the same ISP. You can use a wide variety of POP client reading software on most platform PC's or MAC's, for example Eudora, Outlook or Netscape.

How POP Works

The server waits for a client to open a connection. When the connection is opened the server sends a greeting message and waits for commands to come from the client. The server responds to each command...