POP3, testing via Telnet
When troubleshooting a POP3 service, it's frequently helpful to use the telnet client to "speak" to the server directly, rather than using a mail client which won't give you the exact responses the server does. In this example, we will use telnet to connect to a POP3 server, log in as a user, and list the number of messages available to the user.
ph34r# telnet localhost 110 Trying 127.0.0.1... Connected to localhost.localdomain. Escape character is '^]'. +OK dovecot ready. USER email@example.com +OK PASS thisismypassword +OK Logged in. LIST +OK 1 messages: 1 354 . QUIT +OK Logging out. Connection closed by foreign host.
Confirmed - the POP3 server answers connections, authenticates users, and can access its mail store - in this case, we can see that there is a message queued up and waiting for delivery. (Note that frequently you may NOT see any messages in the queue on a POP3 server, as most organizations using POP3 expect users to download their mail and delete it as soon as they have.)