reading only new messages in imaplib

[Raghul]

eceived: from web50
Received: by twmail.
Received: from mail.
Received: from mail.
Received: by twmail.
Received: from adams
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: from ns2.T
Received: by twmail.
Received: by twmail.
Received: from chat3
Received: by twmail.
Received: by twmail.
Received: from CRM (
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: by twmail.
thread-index: AcUTaP
Received: by twmail.
Received: from web60
Received: from web60
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: from ablis
Received: by twmail.
thread-index: AcUXP/
Received: from web50
Received: from mta.n
Received: from ns2.T
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: by twmail.
Received: from ns2.T
Received: by twmail.


it prints something like this. what it actually display.And pls tell me
what it actually does? I can't understand