There are many factors involved in migrating to or co-exist (Hybrid) with O365. Every organization has or can difference experience based on their current messaging setup. Your existing Exchange environment has to be at some standard or meet some criteria before you start moving to Office Email Cloud. For example if you an undamaged (no mailbox quota, unlimited public folder etc) exchange then first you need to do some cleanup before you move to O365 (Hybrid or Cutoover). There are some basic building blocks you need to follow

Estimating Bandwidth Usage

There are many variables to consider when estimating network traffic. Some of these variables are:

  • The Office 365 service offerings that your organization has subscribed to.
  • The number of client computers in use at one time.
  • The type of task each client computer is performing.
  • The performance of your Internet browser software.
  • The capacity of the network connections and network segments associated with each client computer.
  • Your organization’s network topology and the capacity of the various pieces of network hardware.

Network Bandwidth Calculators you can use with Office 365

 There are calculators available to assist you with estimating network bandwidth requirements. These calculators work for on-premises as well as Office 365 deployments. You can use the Exchange client network bandwidth calculator to estimate the bandwidth required for a specific set of Outlook, Outlook Web App, and mobile device users in your Office 365 deployment. With the Lync Server 2010 and 2013 bandwidth calculator, you enter information about users and the Lync Online features you want to deploy, and the calculator helps you determine bandwidth requirements.

Migration Velocity Testing

Testing and validating your Internet bandwidth (download, upload, and latency constraints) are vital to understanding how to achieve high-velocity migration of on-premises mailbox content to the Office 365 and Exchange Online environments. Slow or latent connectivity reduces the number of mailbox migrations that can be completed during a migration window. Be sure to perform the following steps:

  • Test and confirm that your organization’s Internet bandwidth can manage the network impact of Office 365 migrations.
  • Assess internal network bandwidth availability for Office 365 migration events.
  • Make use of available network tools such as:
  • Determine your download, upload, and latency between your on-premises environment and the nearest Microsoft cloud services data center. The following activities can help with this task:
    • Ping to determine the IP address of the nearest Microsoft cloud services data center from your location.
    • Consult a third-party IP mapping website (for example, to determine that data center’s location.
    • Use a speed test website (for example, to determine the upload, download, and latency statistics between your on-premises environment and the nearest location to the Microsoft cloud services data center.
    • Determine the periods in which the on-premises Exchange system is heavily used (for example, during backups).


Strategies to Improve Migration Velocity

To improve migration velocity as well as reduce your organization’s bandwidth constraints, you should consider the following:

  • Reduce mailbox sizes. Smaller mailbox size improves migration velocity.
  • Public Folder Cleanup – make sure cleanup your public to meet the public folder mailbox in O365
  • Use the mailbox move capabilities with an Exchange hybrid deployment. With an Exchange hybrid deployment, offline mail (.OST files) does not require re-download when migrating to Exchange Online. This significantly reduces your download bandwidth requirements.
  • Schedule mailbox moves to occur during periods of low Internet traffic and low on-premises Exchange use. When scheduling moves, understand that migration requests are submitted to the mailbox replication proxy and may not take place immediately.

For more detailed information, see Exchange Online Migration Performance and Best Practices.