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Help Center Home Power365 Platform Tenant-to-Tenant Directory Sync Migration for Active Directory Support

Cloud Mailboxes

Power365 Mail and Integration Projects have the capability of migrating cloud mailbox and mailbox archive content from one Microsoft 365 tenant to another. The following questions will provide insights into the additional capabilities around mailbox migrations.


What type of content can be migrated?  

The Power365 Migration Engine can migrate the following Mailbox content types:

  1. Email
  2. Calendar
  3. Contacts
  4. Tasks
  5. Notes
  6. Deleted Items
  7. Rules
  8. Automatic Replies
  9. Signatures (Requires Desktop Setup Pro)


What type of filtering options are available?  

Mailbox Content can be filtered both by content type and age filters. The following list outlines all the available Migration Profile filter options.

  • Content Type
  • Date Range
  • Age of Item
  • By Size


Can I schedule Mailbox Migrations?  

Yes, Power365 provides the ability to schedule the start of a sync, the sync interval (hours, days, weeks) and number of syncs (The number of syncs is unlimited, however there is a 100-sync throttling policy. The policy can be adjusted if required, upon a valid request to Support.).


Are Archive Mailboxes Supported?  

Yes, if the source mailbox has an attached archive mailbox, the content will be automatically migrated. However, if the destination environment does not have the proper licensing for archive mailboxes then it cannot be enabled or migrated. Proper licensing is required in the destination environment to migrate archive mailboxes.

For more information, review the Microsoft Exchange Online Archive plans.


Are Shared and Room Mailboxes Supported?  

Yes, all cloud based mailboxes and mailbox archives are supported. Regardless if they are synchronized with a local AD user or not.

Cloud only Shared, Equipment or Room mailboxes must be migrated using a Mail with File or Mail with Discovery Project Type.


Can I migrate Local Exchange Mailboxes?  

Yes, the Basic Migration project type supports this functionality. For more information, see the additional information links listed later in this article.


Are Permissions and Delegation Migrated?  

Yes, Mailbox Permissions and Folder Permissions are migrated if the destination user exists and has been matched with the Power365 Project executing the migration. There are various access rights that can be assigned to a Mailbox which can be migrated. Those are:

  1. Access Right Levels –  Access Rights specify the permission assigned to the user on the mailbox. The supported parameters are:

         • Change Owner – Change Owner allows a delegate to modify mailbox owner permissions.

         • Change Permission – Change Permission allows a delegate to modify another users’ permission.

         • Delete Item – Delete Item permission allows a delegate to open this mailbox but only delete content. No editing or creation is allowed.

         • External Account – External Account allows a delegate from an outside organization to open this mailbox.

         • Full Access – Full Access permission allows a delegate to open this mailbox and behave as the mailbox owner.

         • Read Permission – Read Permission allows a delegate to open this mailbox but only read content. No editing or creation is allowed.

  2. Send on Behalf – Send on Behalf permission allows the delegate to send email on behalf of this mailbox. The From line in any message sent by a delegate indicates that the message was sent by the delegate on behalf of the mailbox owner.

  3. Send As – Send As permission allows a delegate to send email from this mailbox. The message will appear to have been sent by the mailbox owner.


What happens to a Message Address during Migration?  

By default, any address found in a mailbox item such as emails and calendar items are translated to the matched target domain. This feature is automatically disabled when the Litigation Hold option is enabled to retain the integrity of the data under hold.

As an example, when the source tenant mailbox user is named and is matched to, any message or calendar item migrated from any mailbox user will have Jon’s email address translated from to

This action is necessary to prepare the user mailbox for reply-ability and permission to modify migrated items.


Can a Mailbox under Litigation Hold be migrated?  

Yes, Litigation Hold settings and data from source mailbox can be copied to the target mailbox. In addition, selective filtering by data type (e.g. EMail, Calendar, Tasks, Notes) is not permitted. For more information on litigation hold, see the additional information later in this article.


How many times can I Sync my Mailbox Content?  

Power365 Mailbox migrations are unlimited by number of pass, mailbox size or mailbox archives. There is no maximum pass count you need to worry about. Sync as much data and as often as you require to meet your project needs.


How do I know my large mailboxes will migrate in time?  

Power365 stages mailbox data prior to user mailbox cutover. Each sync after the initial sync is a delta synch of the email content. When the user is ready to cutover, the final mailbox delta sync will complete, ensuring the latest changes have been copied to the destination mailbox. By staging data in a prepared mailbox, Power365 guarantees large mailboxes will be ready for cutover when the event is scheduled.


What throughput can I expect during migrations?  

The general rule of mailbox migrations is that the more complex the content and the size of the source, the longer it will take to complete the initial synchronization. However, with multiple-passes only delta changes are migrated after the initial job, which increases the overall performance and cutover flexibility. Once the mailbox is synchronized initially, it is ready for the User to complete the Outlook cutover process, if applicable. Therefore, migration throughput isn’t as much of an issue when prestaging the data before the end-user is cutover.

The reported migration throughput on average is approximately 1 GB an hour.


How many migrations can I run at once?  

When pre-staging mailbox data, users can be batched in waves and their initial synchronization can be managed and scheduled to start and complete, preparing it for the scheduled cutover date.

By default, Power365 can migrate up to 200 mailboxes simultaneously. However, this can be extended in some cases upon validated request to support.


Should I disable Calendar Repair Assistant in Microsoft 365 during Power365 Mailbox Migrations?  

Calendar Repair Assistant (CRA) in Microsoft 365 may have adverse impact on meetings and recurring meetings after migrations. It is recommended that CRA be disabled during the start of any (sync job) migration. This service may be enabled after the migration has been successful concluded and the end-user has been cutover to the destination. There is no known negative impact when Calendar Assistant is disabled temporarily.

Use PowerShell (PS) to create a remote session to Microsoft 365 tenant then execute the following commands:

Get-Mailbox -ResultSize unlimited | Set-Mailbox -CalendarRepairDisabled $true

The Calendar Assistant is now disabled for all mailboxes in the Microsoft 365 tenant. It can be enabled again by using this PS command:

Get-Mailbox -ResultSize unlimited | Set-Mailbox -CalendarRepairDisabled $false


Additional Information  

User Migration Process

Migration Profiles

Migration Waves

Litigation Hold

On-Premises Migration




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