As part of a broader investigation, we measured the network costs between Enterprise email clients and Exchange 2007 SP1. The values presented here might help you get a ball-park value for the network requirements connecting your datacenter to your users. The clients we considered were: Outlook 2007 Online mode; Outlook 2007 Cached mode; Outlook 2007 Cached mode via RPC/Http (Outlook Anywhere) and Outlook Web Access. We are not reporting the network bytes passed between Exchange roles, but the bytes entering and leaving the 'datacenter.' Outlook Anywhere and Outlook Web Access connect to the 'Client Access Server' role, while Outlook 2007 (in both Online and Cached mode) connects directly to the 'Mailbox' role. The network traffic from earlier Outlook versions can be estimated from the Exchange 2003 results, published in the whitepaper http://www.microsoft.com/technet/prodtechnol/exchange/2003/clinettraf.mspx, as there haven't been fundamental changes in the Exchange-Outlook communications in the 2007 releases.
Our user profile started with the message send and delivery rates from the 'light, medium, heavy and very heavy' knowledge worker profiles. We further assumed: an average message size of 50kB; that every message delivered was read; and half of the incoming mail was deleted. Our Web client logged in - logged off twice/day, while we neglected the logon – logoff costs from the other clients. (Enterprise email users tend to stay logged in for days at a time.)
Exchange Server 2007, Exchange 2007, Network, Traffic, Client Access