What is the Caching policy for IMAP accounts

Hello,

I have configured an IMAP account in my Outlook 2003. I have observed that
some of the emails in the IMAP account are still accessible in Outlook, even
when i am not connected to the network. This does not happen always, and
each time a different set of emails is accessible.

This leads me into thinking that Outlook is caching some of the emails
according to some policy like:
-- most frequently accessed emails
-- most recently accesed emails
-- newly arrived emails

My question is what is the caching policy that Outlook uses for emails from
am IMAP account? Is there a way to configure this?

--
Darshan