long wait to open message

I'm using outlook and have set up my laptop so that I can
Retrieve email from the exchange 2000 server from a
remote location. I have also set up outlook so that
messages will synchronize with the server and store
locally onto the laptop. When I'm connected to the
internet via a dialup 56k modem I open a message with an
attachment that is stored locally, however the message
takes a long time to open. I don't understand why because
the message is stored locally and nothing needs to be
downloaded onto the laptop anymore. I think outlook is
still downloading the same message from the Exchange
server. How do I set up the laptop or server so that when
a remote user accesses local stored emails, it wont take
such a long time to open it.