Protocols > Post Office Protocol v3 (POP3)

POP3, or the Post Office Protocol v3, is a protocol for retrieval of mail from a central mail server.  The two most common protocols for this type of activity are POP3 and IMAP.  The major difference between these two protocols is that POP3 does mail retrieval down to the local system and the message is removed from the central server (unless settings are changed), while IMAP leaves all the messages on the central store.  This allows for IMAP clients to be able to roam with their full mailbox available no matter what device they are checking mail from.  Regardless, here are some operational basics on how HiPPIE is identifying POP3.

Protocol Handshaking

POP3 has a very identifiable handshake as a part of the protocol.  When a POP3 client connects to the server, the first thing that occurs is that the server responds with a banner along the forms of the ones shown below.  Regardless, they all follow the general form listed below that. 

• +OK Hello there.
• +OK hello from mypop3host.

General form: +OK <some hello statement>

After the server has generated this hello to the client, the client will respond by sending its username to the server.  This follows a very simple form listed below.  When those two pieces of information have gone in both directions (hello to the client, and username to the server), we can ascertain that this connection is a POP3 connection and stop worry about what further occurs.

USER <username>