Flow diagram of the MailUtl3
(C) 2007 Fumio Kawamata

      S Wait for connection on TCP port 110
   P    Wait for connection on TCP port 123
C->P    Open connection to localhost, port 123
C<-P    +OK Welcome to the MailUtl3 Version 3.0.0.9
C->P    USER UserName#ActualPOP3Server:110;D:\home\MailUtl3Config-MyISP.ini
C<-P    +OK Password required
C->P    PASS ********
   P->S Open connection to actual POP3 server, port 110
   P<-S +OK JPOP server ready (jpop39) <1043272.1173961152724@ActualPOP3Server>
   P->S USER UserName
   P<-S +OK please send PASS command
   P->S PASS ********
   P<-S +OK your maildrop has 2 message(s)
   P->S CAPA
   P<-S +OK Capability list follows
   P<-S TOP
   P<-S UIDL
   P<-S USER
   P<-S STLS
   P<-S LOGIN-DELAY 10
   P<-S PIPELINING
   P<-S IMPLEMENTATION Courier Mail Server
   P<-S .
   or server replies negative response as follow
   P<-S -ERR no such command or illigal state
C->P    STAT
   P->S STAT
   P<-S +OK 2 64000
C<-P    +OK 2 64000
C->P    LIST
   P->S LIST
   C<-S +OK scan listing follows
   C<-S 1 32000
   C<-S 2 32000
   C<-S .
C<-P    +OK scan listing follows
C<-P    1 32000
C<-P    2 32000
C<-P    .
C->P    RETR 1
   P->S TOP 1 20
   P<-S +OK message follows
   P<-S Return-Path: xxxxxx
   P<-S Received: from xxxxx
     |
   P<-S
   P<-S Mail body
   P<-S .
   P->S RETR 1
   P<-S Return-Path: xxxxxx
   P<-S Received: from xxxxx
     |
   P<-S
   P<-S Mail body
   P<-S .
C<-P    Return-Path: xxxxxx
C<-P    Received: from xxxxx
     |
C<-P    X-MailUtl3-Sender-IP-Address: xxx.xxx.xxx.xxx
C<-P    X-MailUtl3-Sender-Hostname: seners.host.name
C<-P    X-MailUtl3-Lookuped-IP-Address: xxx.xxx.xxx.xxx
C<-P    X-MailUtl3-Status: Reverse lookup failure
C<-P
C<-P    Mail body
C<-P    .
C->P    DELE 1
   P->S DELE 1
   P<-S +OK Message 1 deleted.
C<-P    +OK Message 1 deleted.
     |
C->P    QUIT
C<-P    +OK Good-bye from the MailUtl3
   P->S QUIT
   P<-S +OK goodbye