POP (Post Office Protocol, Ver 3)
POP, which is similer to SMTP, involves command/reply lockstep protocol. Unlike SMTP, POP is used to retrieve mail for a simple user, typically the POP server has access to a database of messages created by an SMTP server. POP connection require authentication in the form of a secret that is shared by the user and the POP server (a Password).
POP commands and replies are formatted as ASCII lines, and all replies start with either “+OK” or “-ERR”. Some of the commands that make up the POP protocol are listed below:
USER specify username.
PASS specify password.
STAT get mailbox status-number of message in the mailbox”.
LIST get a list of messages and sizes, one per line , termination line contains just a period.
RETR retrieve a message.
DELE mark a message for deletion.
QUIT remove mark messages and close the TCP connection.