MS Exchange Question

Howdy,

So my brother in-law has a very old server running exchange to handle their mail in the office. I finally convinced them to switch to a web based mail client so I could help manage it… who knows the last time they upgraded/patched/protected the exchange server…

anyway, my questions are:
When using exchange and Outlook, is the mail downloaded locally or is it all stored on the server? ie if I dropkick the exchange server down the stairs, will all mail be lost? If the mail is stored on the server, is there a setting to download it locally?

Cheers.
PB/E/D