Minimal POP3 Commands:
USER name valid in the AUTHORIZATION state
PASS string
QUIT
STAT valid in the TRANSACTION state
LIST [msg]
RETR msg
DELE msg
NOOP
RSET
QUIT valid in the UPDATE state
Optional POP3 Commands:
APOP name digest valid in the AUTHORIZATION state
TOP msg n valid in the TRANSACTION state
UIDL [msg]
POP3 Replies:
+OK
-ERR
Note that with the exception of the STAT, LIST, and UIDL commands, the reply given by the POP3 server to any command is significant only to "+OK" and "-ERR". Any text occurring after this reply may be ignored by the client.