A funny analogy posted on slashdot.
If the same method that exchange/outlook uses to store email were used in the real world as a paper filing system: Every document is translated into Greek, and the original is burned. Then they are all glued together into one solid block and stuffed into a magic box with a tiny slot, through which you can talk to a little gnome who somehow gets each message for you as needed. Sometimes the gnome gets confused and it takes hours (sometimes days) for him to sort things out; meanwhile he can’t find your documents until he is totally finished becoming unconfused again. As an added bonus the gnome costs several thousand dollars and when he dies every few years you need to buy a new gnome. Oh and if the first box gets (arbitrarily) full you have to buy another special gnomebox, which of course costs $$$
Disclaimer: I don’t think exchange is all bad, but I think it could be much better and certainly more open.