Configuring Microsoft 365 Archiving Policy

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Each Microsoft 365 user with a license that includes Exchange Online Archiving can use an archive mailbox (Online Archive). An archive mailbox is a separate mailbox associated with the user’s primary mailbox and is available in Outlook and Outlook on the web.

Users can use the archive mailboxes along with their primary mailboxes. If your mailbox has become too large and you cannot receive/send emails, you can config automatic archiving in an Online Archive.

Important. Note that Online Archive is not a backup. Exchange Online Archiving is designed to provide additional mailbox storage and support retention/lifecycle management; it does not provide a point-in-time backup/restore capability. You should not rely on the Online Archive as your only protection against accidental deletion, corruption, or other data-loss cases. Use Microsoft 365 retention/hold capabilities and, where required by your organization’s recovery requirements, a separate backup solution.

Key Behavior and Limitations

Archive Policies in Microsoft 365 allow you to define rules for when your email items will automatically move from your mailbox to the Online archive. By default, archive mailbox data requires an Internet connection. In cached Exchange mode, items from the archive are not downloaded locally (unless configured).

Also, when searching in a mailbox, archive mailbox items may not always appear in search results by default (depending on the Outlook version, search scope, and cache settings).

Exchange Online Archive Eligibility

Not all Exchange mailboxes are eligible for online mailbox archiving. The eligibility and maximum archive mailbox size depend on your license.

• With Microsoft 365 Business Basic, Standard, and E1 base licenses, the archive mailbox size is limited to 50 GB;
• Auto-expanding archiving provides additional archive storage when the initial 100-GB archive capacity is reached. Storage is added incrementally until the archive reaches a maximum of 1.5 TB. Admins cannot manually increase/adjust the archive storage quota.

Enabling Exchange Online Archive Mailbox

By default, Online Archive is not enabled for all Microsoft 365 users, even those with the appropriate license. You can turn the online archive on or off through the Exchange Admin Center or Exchange Online PowerShell.

Using the Exchange Admin Center to Enable Archive Mailbox

1. Log in to the Exchange Admin center.
2. Navigate to Recipients > Mailboxes and click the mailbox to manage.
3. Click the Others tab and Manage mailbox archive.
   
4. Here you can turn Exchange Online Archiving on or off. The Name field is optional.
   Once enabled, you’ll see the archive mailbox statistics on this page. If you did not customize the archive mailbox name, Exchange may use the “In-Place Archive –” naming convention for the archive mailbox.
   

   

Using the Exchange Online PowerShell to Enable Archive Mailbox

You can also enable Online Archive using PowerShell:

1. Connect to Exchange Online PowerShell:
   

   Connect-ExchangeOnline

   Note. Keep in mind that Exchange Online PowerShell requires the ExchangeOnlineManagement module and supports Modern Authentication (MFA). Legacy authentication is not supported!
   
2. Run the below command to enable the Exchange Online archive mailbox for the specified user:
   

   Important note. Before enabling the archive, you need to ensure that you assigned the appropriate license for the users. Without a valid license, the storage will be limited to 50 GB.

   Enable-Mailbox -Identity fotis.albert -Archive

   
3. Once the Online Archive is enabled, you can enable auto-expanding archiving for the mailbox:
   

   Enable-Mailbox -Identity fotis.albert -AutoExpandingArchive

   To verify that auto-expanding archiving is enabled, run:
   

   Get-Mailbox -Identity fotis.albert | Select-Object ArchiveStatus, AutoExpandingArchiveEnabled

   Important. Keep in mind that Auto-expanding archiving is a permanent setting. After you enable it for a specific user/organization, it cannot be disabled, and admins cannot manually adjust the storage quota for auto-expanding archiving. You need to make sure this feature is required for your organization’s mailbox storage strategy before enabling it.
4. A separate ”Online Archive – User” mailbox will appear in the Outlook client and Outlook Web App.
   

   Note that in Outlook, the archive mailbox appears as a separate mailbox. Of course, as a user you browse it like a regular mailbox, but keep in mind that items are stored in Exchange Online and are not cached locally by default in Outlook cached mode (depending on sync settings).

   

You can enable archive mailboxes for all licensed users at once:

Get-Mailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited |
Where-Object {$_.ArchiveStatus -eq "None"} |
Enable-Mailbox -Archive

In case you’re working with large tenants, you should avoid running unrestricted bulk mailbox modifications against thousands of mailboxes in a single operation. Exchange Online PowerShell is subject to service throttling and transient failures. First inventory the target mailboxes, verify licensing and exclusions, then process users in controlled batches and review failures before continuing.

Hint. Note that the Archive folder inside a mailbox is not the same as the Online Archive mailbox! The Archive folder is a standard mailbox folder, while Online Archive is a separate mailbox database stored in Exchange Online.

How to Use Archive Mailbox

Users can manually move items from the primary mailbox to the Online Archive. In Outlook, select an email, right-click it, and choose Move > Online Archive.

How to Assign Archive Policy

They can also apply archiving policies for a more streamlined and automated approach.

Four archiving policies that can be applied to mailbox folders are available. Select the folder to which you want to apply the archive policy to, right-click on it, and select the Archive Policy you need:

• Personal 1 year move to archive
• Personal 5 years move to archive
• Personal never move to archive
• Use parent folder policy
  

Note. Folder-level “Archive Policy” in Outlook is a client representation of Exchange MRM retention tags applied server-side.

Creating a New Microsoft 365 Archiving Policy

Important. Note that our article focuses on Exchange Online MRM (Messaging Records Management) archive policies that move items to the Online Archive mailbox. These policies are different from Microsoft Purview Retention Policies and Retention Labels (which are used for compliance, records management, and data lifecycle governance across Microsoft 365 workloads).

The out-of-the-box archive policies are few and insufficient for some organizations. But an Exchange Online administrator can create additional archiving policies for Outlook using the Microsoft 365 Admin Center or using PowerShell.

Suppose you want to create a new archiving policy that automatically moves items to the user’s Exchange Online Archive mailbox.

Here’s the process using PowerShell:

In the example below, we use -Type All in order to create a Default Policy Tag (DPT) that automatically moves eligible mailbox items older than 90 days to the Online Archive. We then add the tag to a custom MRM retention policy rather than modifying the built-in Default MRM Policy. Run the following command to create a new archiving policy that automatically moves eligible items older than three months to the Online Archive:

$policyTag = "Default 3 Month Move to Archive"

New-RetentionPolicyTag $policyTag `
-Type All `
-RetentionEnabled $true `
-AgeLimitForRetention 90 `
-RetentionAction MoveToArchive

This command creates a new Default Policy Tag (DPT) that moves eligible items older than 90 days to the Online Archive.

Now that the retention tag has been created, add it to a custom MRM retention policy. You should avoid modifying the built-in Default MRM Policy unless you intentionally want to change the archive behavior for all mailboxes that use that policy.

$policyName = "Corporate Archive Policy"

New-RetentionPolicy -Name $policyName `
-RetentionPolicyTagLinks $policyTag

Now assign the custom MRM retention policy to the mailboxes that should use the 90-day archive rule:

Set-Mailbox -Identity user@domain.com `
-RetentionPolicy "Corporate Archive Policy"

Now check if the mailbox is using the expected MRM retention policy and that its Online Archive is enabled:

Get-Mailbox -Identity user@domain.com |
Format-List RetentionPolicy,ArchiveStatus

Note. You should explicitly assign a custom MRM retention policy to the mailboxes that should use it. Keep in mind that creating a retention policy does not automatically assign it to users.

The Managed Folder Assistant (MFA) processes mailboxes asynchronously in the background. After assigning/changing an MRM retention policy, processing is not necessarily immediate. For testing or troubleshooting, you can manually trigger processing for a specific mailbox:

Start-ManagedFolderAssistant -Identity user@domain.com

Allow some time for processing to complete, after that you need to verify the mailbox and archive statistics.

Hint. In Microsoft 365, you can also configure Microsoft 365 retention policy which defines when an email will be deleted.

Conclusion

Configuring a Microsoft 365 archiving policy is crucial for effective data management and compliance. Our blog post explored the steps involved in setting it up.

By understanding retention tags, policies, and actions, organizations can customize their archiving policies to meet their specific needs.

Regular monitoring and user education are essential for maintaining policy effectiveness. A well-configured archiving policy ultimately promotes responsible data management, regulatory compliance, and improved data governance.