Is Exchange 2003 a bandwidth consumer? :)
For those of you who are looking for an answer to this question, I recommend you to review Network Traffic Statistics on Exchange 2003 results, you'll find this document very useful. Year to year this document is reviewed and updated by Christophe Leroux (MCS Consultant). It contains the description of the tested scenarios (you can apply those in your current organization and get your own results), comparison between different versions of Outlook, OWA traffic is also included, RPC over HTTP, traffic generated against public folders and MORE.
It's a good reference if your main concern is: how my network bandwidth is going to be affected once migrated to Exchange 2003?? hope you find it useful as I did.
Client Network Traffic with Exchange Server 2003
If you want to improve your bandwidth utilization... deploy Exchange 2003 and Outlook 2003 in your organization (cache-mode enabled), that combination will optimize your network usage, improve the user experience, and provide a more robust solution helping the administrators to reduce the numbers of incidents due network connectivity issues.