Sometimes I wonder why large organisations need to run Exchange as an enterprise solution. I think the prime reason is the address book. all the other stuff, calendering, PF or doc share, etc is all very much secondary and is usually local. On the basis that 'small is beautiful' (or at least relatively small), how about architecting the next version so the address book function becomes hierarchical, ah la DNS, infinitely expandable, but with the ability to be seperate from the actual transmittal and storage of mail. This would allow large corporations to be more flexible in terms of upgrades and general management, since it would be a smaller footprint... Yet the ability to lookup addressees is maintained...