Migration of Exchange archive mailboxes larger than 100 GB

Problem:

You are migrating archive mailboxes (In-Place Archives) using CodeTwo migration software and would like to identify and learn how to migrate mailboxes that are larger than 100 GB.

Solution:

By default, the storage quota for Exchange archive mailboxes is 100 GB (50 GB in Microsoft 365 Business Basic and Standard plans). This means that in order to migrate archive mailboxes that are larger than 100 GB, you need to prepare your target server accordingly:

• Exchange Online (Microsoft 365) – you need to enable auto-expanding archiving to increase the storage limit to up to 1.5 TB.

  Important

  According to Microsoft's documentation, it can take up to 30 days until additional storage space (another 100 GB) is provisioned for archive mailboxes in Exchange Online. This means that the migration of archive mailboxes larger than 100 GB can take 30 days or more, depending on the size of your source archive mailboxes.

  You can also enable auto-expanding archiving for specific users only to quickly increase the storage quota of their archive mailbox by 10 GB. Learn more

• Exchange Server – there is no maximum storage limit for mailboxes in on-premises Exchange, but you need to manually increase the storage quota for archive mailboxes.

Use the links below for more details:

• Which version of CodeTwo migration software supports archive mailboxes?
• Which Exchange licenses allow you to create archive mailboxes?
• How to identify archive mailboxes larger than 100 GB on your source server
• How to prepare a target server for the archive mailbox migration
• How to configure CodeTwo software for archive mailbox migration
• Troubleshooting the migration of archive mailboxes

Which version of CodeTwo migration software supports archive mailboxes?

To migrate archive mailboxes, you need to use CodeTwo Office 365 Migration or CodeTwo Exchange Migration version 3.2.10.x or newer. You can download the latest version of the software here:

• CodeTwo Office 365 Migration
• CodeTwo Exchange Migration

Which Exchange licenses allow you to create archive mailboxes?

Exchange Online

If you intend to migrate archive mailboxes larger than 100 GB, you need to have an Exchange Online Plan 2 license or an Exchange Online Plan 1 license with an Exchange Online Archiving add-on license. Only these licenses support the auto-expanding archiving feature, which needs to be enabled in your target Microsoft 365 tenant (as described later in this article) to increase the storage limit of your archive mailboxes from 50/100 GB to up to 1.5 TB.

Go to this Microsoft article for the complete list of Exchange Online / Microsoft 365 plans that support email archiving.

Exchange Server

To be able to create archive mailboxes on your target on-premises Exchange server, you need to have access to the In-Place Archive feature, which requires the Exchange Enterprise client access license (CAL). Learn more

How to identify archive mailboxes larger than 100 GB on your source server

Using PowerShell, you can easily check if there are any archive mailboxes on your source server that exceed the quota of 100 GB:

1. First, connect to your Exchange server via PowerShell by following the steps provided in this article.
2. Run the following cmdlet:

   $archivemailboxsize = (Get-EXOMailbox | Get-EXOMailboxStatistics)

   to save the current archive mailbox data into a variable.

   Important

   The Get-EXOMailbox and Get-EXOMailboxStatistics cmdlets are available only in the Exchange Online PowerShell module. To get the same results but from your on-premises Exchange environment, use Get-Mailbox and Get-MailboxStatistics instead.

3. To retrieve that data and to sort archive mailboxes by size (from the largest to the smallest, as shown in Fig. 1.), use this cmdlet:

   $archivemailboxsize | select DisplayName, TotalItemSize | sort -Property TotalItemSize -Descending‎

Fig. 1. All archive mailboxes from a single Microsoft 365 tenant listed from the largest to the smallest.

How to prepare a target server for the archive mailbox migration

First, make sure that archive mailboxes exist on your target server. See this Knowledge Base article to learn how to enable archive mailboxes in Exchange Online or Exchange Server.

The next steps depend on your target environment:

• Exchange Online – enable auto-expanding archiving
• Exchange Server – increase the storage quota for archive mailboxes

Enable auto-expanding archiving in Exchange Online

1. Connect to Exchange Online PowerShell by following the steps provided in this article.
2. Enable auto-expanding archiving for:
   1. the entire organization by running the following cmdlet:

      Set-OrganizationConfig -AutoExpandingArchive

   2. a specific user by running the following cmdlet:

      Enable-Mailbox <user mailbox> -AutoExpandingArchive 

      Remember to replace <user mailbox> with the user's UPN.

Increase the storage quota for on-premises Exchange archive mailboxes 

1. Open the Exchange Management Shell.
2. Increase the storage quota of an archive mailbox for:
   1. a specific user by running the following cmdlet:

      Set-Mailbox -Identity <user mailbox> -ArchiveQuota unlimited -ArchiveWarningQuota unlimited

      Remember to replace <user mailbox> with the user's UPN. 
   2. multiple users by running the following cmdlet:

      $users=Import-CSV <filepath>
      foreach($user in $users){Set-Mailbox -Identity $user.UPN -ArchiveQuota unlimited -ArchiveWarningQuota unlimited}

      Remember to run the lines of the code one by one. Replace <filepath> with a path to a CSV file that contains a list of UPNs of the users for whom you want to increase the archive mailbox storage quota (e.g. C:\users.csv). In this example, the header of the column (in the CSV file) that lists UPNs is UPN. If your column's header is different, update the code above accordingly.

Set-Mailbox -Identity <user mailbox> -ArchiveQuota 500GB -ArchiveWarningQuota 490GB

How to configure CodeTwo software for archive mailbox migration

Go to the user's manual of your CodeTwo product for detailed instructions on how to configure a migration job:

• CodeTwo Office 365 Migration
• CodeTwo Exchange Migration

There are a few things to note:

1. In the Mailbox types step of the migration job configuration wizard, be sure to select one of the options that will let you migrate archive mailboxes (Fig. 2.).

Fig. 2. To migrate archive mailboxes, you need to select one of the options marked in the figure above.

2. When migrating mailboxes by using a CSV file, be sure to include the Mailbox Type column and use the Archive value for archive mailboxes. Learn more
3. In the Match mailboxes window, you can use the Automatch option to let the program match source and target mailboxes (primary and archive) automatically, as described in this article. You can also match mailboxes manually, e.g. if you want to match an archive mailbox from the source environment with a primary mailbox from the target environment.
4. Configure the Scheduler to run automatic delta migrations (Fig. 3.). That way, after the initial migration is completed, the program will automatically attempt to migrate the remaining data from the source server at specified time periods (the already migrated items are skipped). This is especially useful when migrating archive mailboxes larger than 100 GB to Exchange Online, as it is very likely that you will run out of storage space for your target archive mailboxes before the auto-expanding archiving is provisioned and additional storage is added (which can take up to 30 days). Learn more about the Scheduler

Fig. 3. Configuring the Scheduler to run automatic delta migrations.

Troubleshooting archive mailbox migration

You got the following notification in your CodeTwo software:

The storage limit for target mailbox '<email address>' has been exceeded.

This means that the indicated target mailbox is full. Proceed accordingly to your target environment:

• Exchange Online (Microsoft 365): be sure to enable auto-expanding archiving for this mailbox to increase its storage quota. Note, however, that it can take up to 30 days until additional storage space (another 100 GB) is provisioned. Learn more
• Exchange Server: increase the storage quota for this mailbox as shown here. 

Once the additional space is added, use Run delta migration in your CodeTwo migration software (as shown in Fig. 4.) to continue migrating remaining data. Learn more about this feature

Fig. 4. The delta migration feature will migrate all items that failed during previous migration run(s).