POP3 protocol summary


POP - post office protocol.

Versions:

  • POP1 - 1984
  • POP2 - 1985
  • POP3 - 1988
  • Updated version of POP3 with additional authentication mechanisms and extensions - 1996
POP3 communication schema

The approach "download and delete":

  • The message storage on the server is a temporary storage for messages.
  • All messages must be transferred to the mail client.
  • After uploading to the client, the messages are deleted from the server.

Advantages:

  • Simple protocol.
  • Letters are available when there is no network connection.

Disadvantages:

  • Only 1 client.
  • Single mail storage (no folders, filters, flags, etc.).

POP3 is an application layer protocol (port 110), it uses TCP transport protocol.

Session states:

  • Authorization - the client introduces himself and confirms that he is who he says he is.
  • Transaction - the client downloads the mail and marks the downloaded message for deletion.
  • Update - the server deletes the marked message and closes the connection.

POP3 works in text mode, interacting in a request-response format.

POP3 responses:

  • +OK - successful command execution.
  • - ERR - error.
 POP3 commands:

POP3 commands
POP3 commands

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