EDIT 5/30/2008: The content of this article has since been published in our official Exchange documentation. Please go here for the most updated version.
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.)
Ave message Size
Messages read /day
Messages deleted /day
OWA logon-logoff /day
The network bytes transferred for each action is independent of mailbox size, so we did not perform separate measurements for each profile, but measured the costs of the actions and summed them for each profile.
Note that for Outlook 2007 in Cached mode and Outlook Anywhere, which work off a local copy of the user mailbox, there is negligible traffic associated with reading or deleting mail - as these actions work against the local copy - but every mail received is downloaded to the client.
In the table below, all values are in Kilobytes/day/user. I've broken out the sending portion from the other actions (labeled as 'aggregate').
Outlook 2007 - Online
Outlook 2007 - Cached mode
Outlook Anywhere 2007
Outlook Web Access
To use these values, suppose you had a Datacenter with 10,000 Medium Outlook Cached mode users. Further assume all these users were in the same time zone, so they did the majority of the work during an 8 hour day.
This would predict the Average network bytes/sec would be
Assuming a daily peak of twice this average value, the network coming into the 'datacenter' would have to support roughly 15 megabits/sec from these users alone.
- Greg Smith