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Summary: In a hybrid environment, migration endpoints bridge Exchange on-premises and Exchange Online for mailbox transfers. Admins can customize concurrent migration settings for efficient migrations between the platforms.

In a hybrid environment where both Exchange on-premises and Exchange Online coexist, migrations are facilitated through the use of migration endpoints when performing manual Office 365 or Exchange Server migrations via the Exchange Admin Center interface. These endpoints serve as connectors that bridge the two platforms, enabling the migration of mailboxes from one deployment to another. Administrators have the flexibility to specify the maximum number of mailboxes to be migrated in each batch from the source to the destination account by configuring the ‘Max. Concurrent Migrations’ settings within the migration endpoint. In this tutorial, we will delve into the details of this process.

First, let us go through the basic stages included in the native migration from Exchange to Office 365.

Migrate mailboxes from Exchange to Office 365 Using Hybrid Configuration

Migration of mailboxes from an on-premises Exchange Server to Office 365 using the hybrid configuration involves the steps:

  1. Create a migration endpoint
  2. Enable the MRX Proxy Service
  3. Move mailboxes using EAC
  4. Remove the migration batch after completion

Thus, migration to the cloud using the hybrid configuration starts with the creation of migration endpoints.

Migration endpoints – why are they important?

Migration endpoints serve as the configuration bridge between Exchange on-premises and Office 365. They encompass critical information like the Fully Qualified Domain Name (FQDN) of the on-premises server, a descriptive name, and login credentials for Exchange Online. To optimize the performance of a migration endpoint, there are several parameters that you can customize based on your specific needs.

  • MaxConcurrentMigrations: this is the number of mailboxes that can be moved from the endpoint. It can be defined by the user, though its default value is 20.
  • MaxConcurrentIncrementalSyncs: The maximum number of concurrent delta synchronizations that can be active simultaneously is defined by this setting. The default value for the default endpoint is 20, whereas for the new endpoint, it is set to 10.

But you can increase the limit for the concurrent mailboxes using the Exchange Admin Center or PowerShell.

Set concurrent limitation using Exchange Admin Center

You have the option to configure the concurrent migration limit when either creating a new migration endpoint or editing an existing one. The following steps outline the procedure for creating a migration endpoint:

  1. Login to Office 365 using administrator account and follow recipients>>migration. Here click the (…) icon and select Migration Endpoint.
  2. At the migration endpoint page, click (+) Add icon.
  3. Choose the first option of Remote Exchange. Click Next.
  4. The Migration Endpoint Wizard requires you to input Email Address, Account with privilege (domain\user name), and password. The account should have administrative rights.
  5. On the next page, input Remove MRS proxy server of your Exchange online account. Click Next.
  6. On the next page, provide a unique migration endpoint name and the options for concurrent migration. The first one is ‘maximum concurrent migrations,’ and the second is ‘maximum concurrent incremental sync.’ Input the desired value and click New.
  7. A new migration endpoint is created with the appropriate value of maximum concurrent migration.

If you have already created the migration endpoint, but you want to alter the value of concurrent migration, then you can change it also. Follow the below steps:

  1. Go to recipient>>migration.
  2. Select the migration batch which you need to change and View details under Associated endpoint. It will open the ‘Edit Migration Endpoint’ window.
  3. In the window, enter the ‘maximum concurrent migrations’ value.
    Note: The limitation of concurrent migration is 300.
  4. Click Save.
Set concurrent limitations using Windows PowerShell

There is a special cmdlet ‘MaxConcurrentMigrations’ to set the concurrent limitation. First, you need to connect the windows PowerShell with Exchange Online and then run the command. Here are the steps:

  1. Start Windows PowerShell as an administrator.
  2. Run the command –
    Set-ExecutionPolicy Unrestricted

    The command will allow you to run any script even if it does not have a digital signature.

  3. Run the command –
    $livecred = Get-Credential

    It will ask you to input the Administrator credentials and place it into the $livecred variable.

  4. Run the command –
    $s = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri -Credential $cred -Authentication Basic -AllowRedirection

    The command creates a session with Exchange Online.

  5. Run the command –
    $importresults= Import-PSSession $s

    The command places the session to the $importresults variable.

  6. Run the command –
    Set-MigrationEndpoint –Identity EndpointName -MaxConcurrentMigrations Value

    Here at the EndpointName, you will input the name of migration endpoint, and at Value, you will input the desired value for concurrent migration.


The ‘MaxConcurrentMigration’ value imposes a restriction on the overall number of mailboxes that can be migrated within a migration batch. Due to the intricacies associated with these settings, Exchange to Office 365 migrations are indeed complex. However, for those seeking a more streamlined and controlled migration process, the Kernel Office 365 migration tool offers a hassle-free solution. With this tool, you simply need to select the source Exchange and destination Exchange Online accounts, provide the necessary credentials, and apply appropriate filters. You can then initiate the migration immediately or schedule it to suit your convenience.