The synchronisation, as i told is that between the folders on your mail
server and those in outlook. Hotmail is an HTTP and probably thats what is
doing it. But it shouldnot be a concern because you have the control over it.
If you go to Tools -> Options -> Mail setup -> send receive , You ll see the
option to send receive every 5 minutes or so. You can configure it the way
you want. What this does is it makes sure that your outlook folders are
updated every 5 minutes ( or as what is the setting)