Set-up your Telnet program to connect to the POP server at port 110 eg. mail-server.fire.net 110 .Once the connection has been established , the POP3 server issues a one line greeting. e.g. +OK POP3 server ready
Responses from the POP3 consist of a success indicator and a keyword possibly followed by additional information. There are two success indicators: positive ("+OK") and negative ("-ERR").
Now you must identify yourself
USER name ( name is the fist part of your email address e.g. name@somehost.somecountry )
LIST ( list how many messages in your mailbox and how big they are)
DELE n (marked messages number n for deleting )
An example
Michael (Michael@gipsy.net) is travelling the world.
Shortly after he arrived in Hong Kong he went to the
local CyberCafe to check his mail
first he telnet his POP server at port 110
+OK POP3 server ready
USER Michael
PASS 2good2be4goten
LIST
RETR 1
Hi Michael
Jane
DELE 1
QUIT
+OK Michael is welcome.
+OK mailbox locked
+OK 1 messages 491 (octets)
1 491
Received: from [194.69.42.108] by mail-server.hk-online.hk Sat, 4 Nov 98 20:24:56 (GMT)
From: Jane@fire.com
To: Michael@gipsy.net
Subject: Trans-Siberian Railway
Date: Sat, 04 Nov 1998 19:23:00 GMT
Reply-To: Jane@fire.com
I'm going to take the Trans-Siberian Railway to
Moscow. If you're interested, meet me in Beijing for the
Chinese new year.
+OK message 1 deleted.
+OK Updated mailbox.
A more detailed explanation on POP3 can be found here
rfc1081: Post Office Protocol - Version 3