A centralised v decentralised Exchange model largely depends on network
bandwidth, network utilisation and probably the biggest factor, network
latency.

Remote users will normally generate between 3 - 5 kbps, Outlook cached mode
can alleviate this as it can reduce the number of bytes on the wire by
between 25% - 50% percent depending on the traffic being sent. i.e. a word
document or excel spreadsheet will compress more than a jpg or a zip file.
Also there are certain things that cached mode cannot help with, have a look
at the Practices to avoid when you use Outlook 2003 with Cached Exchange
Mode section in
http://support.microsoft.com/default.aspx?scid=kb;en-us;870926. Also take a
look at http://office.microsoft.com/en-us/assistance/HA011402591033.aspx

When you say each political unti could administer their own set of
mailboxes, do you mean Exchange servers ?

Regards

Paul Ford
Edge IT Ltd