This question was from a university in Chicago adopting Office 365 for faculty, staff, and students.
The first data point you need to gather before you can determine client bandwidth required for Exchange Online is what is your mailbox usage profile? Are your users light, medium, heavy, or very heavy email users? How can you determine this?
If you have Exchange 2003/2007/2010 on prem you can use a tool called the Exchange Profile Analyzer to run against your infrastructure to gather this crucial data point. See my other blog post here for more info.
If you migrating from another email system, you will have to gather some mail usage data points either manually or using other message profile statistics. Once you gather the data points you can associate it with the daily mail profile in the matrix below.
Here is a usage matrix we use to determine the mailbox usage profile:
What are the default bandwidth profiles?
After you gather your mailbox usage profile data based on above, you need to associate it to a light, medium, heavy bandwidth profile. This data was gathered by our internal teams and is still being finalized but it will provide you a rough estimation of bandwidth required for your institution.
Exchange Online Light email user profile bandwidth
Exchange Online Medium email user profile bandwidth
Exchange Online Heavy email user profile bandwidth
Exchange Online Very Heavy email user profile bandwidth
New released Exchange Bandwidth calculator
We just shipped a very useful Exchange bandwidth calculator you can use with on prem Exchange 2010 or Exchange Online.
Download the newly released beta Exchange client network bandwidth calculator here.
Download the newly released Exchange client network bandwidth guide here.
Plug in the numbers based on the site user mail profile determined above. NOTE: make sure you only use Outlook Anywhere cached (OA-cached column) and OWA 2010 column for Exchange Online. The other columns apply to Exchange on prem only.
Bandwidth estimation examples:
If I have a school that has 3000 Outlook 2010 light users and 1000 Outlook Web App light users connecting to Exchange Online. What estimated bandwidth do I need?
6.4 Mb/s Exchange to client traffic and .99 Mb/s client to Exchange.
If I have a school with 50,000 faculty,staff and students with 8000 Outlook 2010 light faculty and 42000 Outlook Web App Light users for students connecting to Exchange Online. What estimated bandwidth do I need?
63 Mb/s Exchange to client traffic and 16.97 Mb/s client to Exchange
What is the recommended maximum network latency?
It recommended your network have no more than 320ms round trip latency.