title: Download POP3 headers from a certain date (Python)
body: <p>I'm trying to write a pop3 and imap clients in python using available libs, which will download email headers (and subsequently entire email bodies) from various servers and save them in a mongodb database. The problem I'm facing is that this client downloads emails in addition to a user's regular email client. So with the assumption that a user might or might not leave emails on the server when downloading using his mail client, I'd like to fetch the headers but only collect them from a certain date, to avoid grabbing entire mailboxes every time I fetch the headers. </p>
  
  <p>As far as I can see the POP3 list call will get me all messages on the server, even those I probably already  downloaded. IMAP doesn't have this problem.</p>
  
  <p>How do email clients handle this situation when dealing with POP3 servers?</p>