Microsoft mentioned that they throttle migration speeds for reasons tied to security and safety. If you are experiencing speed issues when migrating to Office 365, there are some things you can do to reduce some of this throttling. One of them is to use impersonation.
MigrationWiz uses delegation by default to log in to individual user mailboxes using administrative credentials you specify on your connector. However, MigrationWiz also supports another elevated access mode called impersonation.
The main advantage to using impersonation instead of delegation is that it reduces throttling and can avoid “connection did not succeed” errors. Instead of using the throttling quota associated with the admin account, impersonation uses the throttling quota associated with each user’s mailbox. To migrate using impersonation:
- Make sure you are using admin credentials at the destination (Office 365)
- Edit your mailbox or connector and reveal advanced options
- In the support only options field, set this: UseEwsImportImpersonation=1
- Save your mailbox or connector
MigrationWiz will automatically run a remote PowerShell command to allow the admin account to login to user mailboxes. Here is the remote PowerShell command we execute when you submit a mailbox for migration:
- New-ManagementRoleAssignment -Role ApplicationImpersonation -User <admin_user_name>