voici un petite connexion utilisant le protocole pop.
En bleu, les textes que j'ai saisis.
En rouge, les textes reçus du serveur.
En vert, des commentaires pour donner quelques explications.

Exemple de code 1
>telnet pop.iprelax.net 110   on se connecte sur le serveur pop3, port 110
Trying 216.167.107.199... 
Connected to pop.hebergement-discount.com.
Escape character is '^]'.
+OK Cubic Circle's v1.31 1998/05/13 POP3 ready 
USER nicolas   nom du compte pop
+OK pop11529 selected
PASS *******  mot de passe
+OK Congratulations!
LIST   la liste des messages
+OK 1 messages (922 octets)
1 922
.  il n'y a qu'un seul message qui fait 922 octets
TOP 1   je récupère juste l'entete du message
+OK 922 octets
Received: by albertine.nfrance.com (mbox pop11529)
 (with Cubic Circle's cucipop (v1.31 1998/05/13) Thu Dec 20 18:47:17 2001)
X-From_: nicoas@iprelax.net  Thu Dec 20 18:27:54 2001
Return-Path: 
Received: from mel-rto3.wanadoo.fr (smtp-out-3.wanadoo.fr [193.252.19.233])
        by albertine.nfrance.com () with ESMTP id fBKHRrM08730
        for ; Thu, 20 Dec 2001 18:27:53 +0100
Date: Thu, 20 Dec 2001 18:27:53 +0100
From: "iprelax.net" 
Received: from andira.wanadoo.fr by mel-rto3.wanadoo.fr; 20 Dec 2001 18:28:05
Received: from coucou (193.251.10.43) by andira.wanadoo.fr; 20 Dec 2001 18:27:49
Message-ID: <3c221fa53c530b62@andira.wanadoo.fr> (added by andira.wanadoo.fr)
subject: coucou

.                                 dans l'entete on trouve entre autre le sujet 
                                  et l'expediteur, cela permet de filtrer 
                                  sans charger tout le message 
RETR 1  je recupère tout le message
+OK 922 octets (autodeleted)
Received: by albertine.nfrance.com (mbox pop11529)
 (with Cubic Circle's cucipop (v1.31 1998/05/13) Thu Dec 20 18:47:24 2001)
X-From_: nicoas@iprelax.net  Thu Dec 20 18:27:54 2001
Return-Path: 
Received: from mel-rto3.wanadoo.fr (smtp-out-3.wanadoo.fr [193.252.19.233])
        by albertine.nfrance.com () with ESMTP id fBKHRrM08730
        for ; Thu, 20 Dec 2001 18:27:53 +0100
Date: Thu, 20 Dec 2001 18:27:53 +0100
From: "iprelax.net" 
Received: from andira.wanadoo.fr by mel-rto3.wanadoo.fr; 20 Dec 2001 18:28:05
Received: from coucou (193.251.10.43) by andira.wanadoo.fr; 20 Dec 2001 18:27:49
Message-ID: <3c221fa53c530b62@andira.wanadoo.fr> (added by andira.wanadoo.fr)
subject: coucou

ceci est un message de demo

.
QUIT  on sort ( j'aurais pu faire 'DELE 1' pour supprimer le message
+OK Was it as good for you, as it was for me?  (clean as a baby)
Connection closed by foreign host.