Answer:

Note: This Knowledge Base article first covers Office 365. To learn how to set impersonation for Exchange 2010+, scroll down to that section.

Office 365:

Big Green IT uses delegation by default to log in to individual user mailboxes using administrative credentials specified on the connector. However, we also support another elevated access mode called impersonation.

Benefits:

Using impersonation, sharing the throttling quota and connection limits associated with a single administrative account stops. Instead, the throttling quota of each user is used to log in to each user mailbox.

Using impersonation:

  • Eliminates most “Connection did not succeed” errors.
  • Allows migration of more mailboxes concurrently.
  • Reduces the impact of throttling and connection limits.
  • Uses an admin account without assigning a license to it.

Steps:

To migrate using impersonation:

  • Use admin credentials at the Destination.
  • Sign in to the Migration account.​
  • Edit the Project and click on Advanced Options.
  • If migrating from Office 365, under Source, checkmark Use impersonation to authenticate.
  • If migrating to Office 365, under Destination, checkmark Use impersonation to authenticate.
  • Click on Save Options.

BigGreen will automatically run a remote PowerShell command to allow the admin account to log in to (impersonate) user mailboxes.

Here is the remote PowerShell command we execute when a mailbox has been submitted for migration:

Enable-OrganizationCustomization

New-ManagementRoleAssignment
-Role ApplicationImpersonation -User

To learn how to run these commands man​ually, click here. This is useful if there are delays from Microsoft and the Powershell command does not run immediately.

Exchange 2010/2013/2016:

BigGreen uses delegation by default to log in to individual user mailboxes using administrative credentials specified on the connector. However, we also support another elevated access mode called impersonation.

Benefits:

Using impersonation, sharing the throttling quota and connection limits associated with a single administrative account stops. Instead, the throttling quota of each user is used to log in to each user mailbox.

Using impersonation:

  • Eliminates most “Connection did not succeed” errors.
  • Allows migration of more mailboxes concurrently.
  • Reduces the impact of throttling and connection limits.

Steps:

To migrate using impersonation:

  • Use admin credentials at the Destination.
  • Sign in to the Migration account.
  • Edit the Project and click on Advanced Options.
  • Under Destination, checkmark Use impersonation to authenticate.
  • If migrating from Exchange 2010+, under Source, checkmark Use impersonation to authenticate.
  • If migrating to Exchange 2010+, under Destination, checkmark Use impersonation to authenticate.
  • Click on Save Options.

For Exchange migrations, to enable the admin account to impersonate users, run this PowerShell command:

New-ManagementRoleAssignment
-Role ApplicationImpersonation -User

More information about this PowerShell command can be found here. ​

Notes:

  • Office 365 doesn’t allow Impersonation to be set for Small Business plans. Therefore, do not select the Advanced Option to use Impersonation, when migrating to or from an Office 365 Small Business Plan.
  • Office 365 plans named “Business Essential” and “Business Premium” do support impersonation. Follow the steps above, under the Office 365 section, to enable support for use of impersonation when migrating from or to “Business Essential” or “Business Premium”.
  • If the above Advanced Options are set to use impersonation on a project, these settings will only become effective for those migrations that are started after saving the settings. Migrations that are already running will be unaffected by any such changes.