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Prepare groups of users for migration to Office 365


Applies to: Office 365 Enterprise

Topic Last Modified: 2014-06-05

Summary: Provides guidance on how to split the users in your organization into groups for migration during each migration window.

Migration groups are the set of users that you migrate to Office 365 during each migration window. Depending on the number of users you have, your organization may require multiple migrations to move all your users to the Office 365 environment.

When defining migration groups, you will want to consider more than just the total size of the included mailboxes. Here are some additional things to keep in mind:

  • Bandwidth considerations. All of the mailbox content must travel from the on-premises mail environment over the Internet to Office 365. You can use the migration tools to determine how much data should be migrated once mailbox reduction has been performed. Based on this information, you should scope the size of your migration groups and schedule migration times to work with your existing network and Internet bandwidth.

  • User groups. When migrating groups of users, it is a best practice to migrate users who communicate with each other frequently. For example, the members of a distribution group or an executive team that uses email to communicate vital information. Schedule your migration groups to ensure that the owners of the mailboxes that are migrated will be available immediately after the migration to validate the success of the migration. This is especially imperative for organizations that have end of month financial, inventory, or other reporting mechanisms that cannot be disrupted. Keep in mind the mailbox and calendaring requirements of shared/delegate mailboxes for executives and other key customer personnel and their assistants. It is important that assistants are able to access the calendars of executives and key staff without delay.

  • User locations. In addition, be sure to migrate users in accordance with the physical buildings they occupy. It makes sense to migrate fourth floor Conference Rooms with users on the fourth floor. For smaller buildings with limited meeting space it may become necessary to survey the rooms that are used on other floors as well to ensure these resources are available as soon as possible.

  • User support. When migrating groups of users, your organization must also consider user support planning and capabilities for the initial period after migration. There will likely be a higher volume of service desk calls just after the migration. It is best practice to distribute migration groups across support teams by location in parallel to increase migration velocity as well as balance service desk call volume.

  • Delegates. When creating your groups, be aware that Office 365 supports migration of delegates. We recommend that mailbox migration of delegates and managers occurs at the same time. For example, the mailboxes for an executive and their administrative assistant should be migrated together. Mailboxes and any delegates must be located on the same Exchange Server infrastructure (both of them with Office 365 or with on-premises Exchange Server) for the highest fidelity and best end-user experience. Delegate permissions must have been added while the mailboxes were on the same premises.

    Make sure that you also have the latest updates for Outlook and directory synchronization.

    For a quick review of who the delegates are, run the following in the Exchange Management Shell.

    Get-mailbox | where {$_.GrantSendOnBehalfTo -gt 0} | ft -autosize alias,grantsendonbehalfto > .\output.txt

  • User mailbox forwarding rules. When identifying users, it’s also important to consider if they have forwarding rules set up on their own mailbox. These users would need to be identified, the forwarding email address documented, and after migration is complete, have mailbox-forwarding re-enabled.

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