Exchange Online MRM Retention Policies vs Microsoft Purview Retention

Exchange Online Messaging Records Management (MRM) is a legacy Exchange feature that remains useful for specific mailbox lifecycle cases. In particular, MRM can automatically move messages from a primary mailbox to an archive mailbox and can apply retention tags to specific default folders.

As for new Microsoft 365 retention and compliance requirements, Microsoft recommends using Microsoft Purview retention policies and retention labels instead of MRM.

Microsoft 365 Retention Policy vs. Retention Tag

On Microsoft 365 you get multiple retention mechanisms depending on the workload and compliance requirements. Keep in mind that the modern retention architecture is based on Microsoft Purview retention policies and retention labels, while Exchange Online still supports legacy Messaging Records Management (MRM) retention policies and tags for mailbox-level lifecycle management.

Retention Policies

A retention policy in Exchange Online is a container that groups retention tags. Note that it can be applied only to Exchange mailboxes and is part of the legacy Messaging Records Management (MRM) system.

Retention Tags

Retention tags define specific actions applied to mailbox items after a retention period. They can:

• Be automatically applied to default folders (RPT)
• Be applied to entire mailbox items (DPT)
• Be manually applied by users (Personal Tags)

Key clarification

Note that unlike Microsoft Purview retention labels, MRM retention tags work only within Exchange mailboxes. They can’t be applied to SharePoint, Teams, or OneDrive. You should treat MRM as a specialized Exchange mailbox lifecycle tool rather than a general-purpose Microsoft 365 retention platform.

Note that Microsoft recommends using Microsoft Purview retention policies and labels for modern compliance scenarios. And Exchange MRM is primarily maintained for backward compatibility and mailbox lifecycle cases.

When to Use Exchange MRM vs Microsoft Purview

Licensing Requirements

Note. You can also check our article, Configuring Microsoft 365 Archiving Policy.

Applying Microsoft 365 Retention Policies in Outlook Web App

Exchange MRM can apply retention settings to default folders through Retention Policy Tags (RPTs), to mailbox items without a more specific tag through a Default Policy Tag (DPT), or manually through personal tags. Note that the Default MRM Policy does not include an RPT that automatically deletes items from the Deleted Items folder. In case your organization requires automatic deletion after a specific period, you must create and add an appropriate retention tag to the MRM policy.

Users can manually assign retention tags to email items and folders in Outlook on the web:

1. First, sign in to the Outlook Web App.
2. Right-click on the folder or email message for which to change retention settings.
3. Click Assign Policy and select a retention tag from the list.

Note that the Retention policy settings are inherited from the parent folder (Use parent folder policy) by default.

Creating Microsoft 365 Retention Policy using Microsoft Purview

Some organizations may need more than the predefined default retention policies and want to add new ones. Here’s an example of how to create a new Microsoft 365 retention policy.

First, log in to the Microsoft Purview admin center and navigate to Data lifecycle management → Exchange (Legacy).

Create a Retention Tag

Suppose you want to create a retention tag that deletes mailbox items after 14 days. Here’s the instruction to create it.

Important. Our example creates a personal retention tag. Keep in mind that it does not automatically config organization-wide deletion of items from the Deleted Items folder. For automatic Deleted Items cleanup, you need to create a Deleted Items retention policy tag (RPT) with the required retention period and add it to the MRM policy assigned to the target mailboxes.

1. Click the MRM Retention Tags tab and click the New Tag button.
   
2. In the “Name your tag” step, enter the tag name and description and click Next. Make your tag name and description unique and easy to identify.
   
3. In the “Application method” step, select the method you prefer to apply the tags. Your options are:
   • Automatically to the entire mailbox — Also known as the default policy tag (DPT). This method automatically applies the retention tag to all items in the mailbox without a retention tag.
   • Automatically to default folder — Also known as the retention policy tag (RPT). This method automatically applies the retention tag to a specified default folder.
   • By users to items and folders (personal) — Also known as personal tags. This method allows users to apply tags to custom folders and individual items in the mailbox.In this example, we’ll choose the option By users to items and folders (personal) and click Next.
     
4. Next, specify the Retention period and Retention action. This example sets the retention period to 14 days and permanently deletes the items.
   
5. Review the retention tag settings. When satisfied with the retention tag, click Submit to create it.
   
6. Lastly, click Done after the retention tag has been created.
   The new retention policy tag now appears in the list.
   

Update the Retention Policy

Once the retention tag has been created, it isn’t readily available for users to select in their mailboxes. If they want to use this retention tag, they must manually add it to their mailbox in OWA by navigating to Settings → Mail → Retention policies → Add new policy.

But that’s not a positive user experience. The better option is for the retention tag to be available to the users without doing these extra steps. The way to achieve that is by adding the retention tag to the existing retention policy.

1. Click the MRM Retention Policies, select the existing retention policy to update, and click Edit.
   
2. Click Add tag.
   
3. Check the box next to the retention tag you created, and click Add.
   
4. Now that the retention tag is added click Next.
   
5. Click Submit to save the policy.
   
6. Finally, click Done.
   
7. Wait until the Managed Folder Assistant has finished processing the mailboxes. Once completed, the user can use the new retention policy tag.
   

Creating Microsoft 365 Retention Policy using Exchange Online PowerShell

You can create and manage Exchange Online MRM retention tags and policies using the ExchangeOnlineManagement PowerShell module. Before connecting to Exchange Online, make sure the module is installed and that your PowerShell version meets the requirements of the installed module.

$PSVersionTable.PSVersion

Get-InstalledModule ExchangeOnlineManagement -ErrorAction SilentlyContinue |
Select-Object Name, Version

If the module is not installed, install it before continuing:

Install-Module ExchangeOnlineManagement -Scope CurrentUser

If an older version is installed, update it according to your organization’s change-management policy:

Update-Module ExchangeOnlineManagement

Connect to the Exchange Online PowerShell session:

Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline -UserPrincipalName admin@contoso.com

Create a Retention Tag

Run this command to create a new retention tag. This retention tag has these settings:

• Name: Permanently Delete Items After 24 Days.
• Type: Personal.
• Retention age: 24 days.
• Action after the retention period: Permanently delete.

New-RetentionPolicyTag "Permanently Delete Items After 24 Days" ` 
-Type Personal -RetentionEnabled $true ` 
-AgeLimitForRetention 24 -RetentionAction PermanentlyDelete

Update the Retention Policy

For users to see the new retention tag in their mailbox automatically, you must add it to their existing retention policy. To do so, run the following commands to add the new retention tag to the default retention policy.

# Specify the retention policy and retention tag. 
$retentionPolicy = 'Default MRM Policy' 
$policyTag = 'Permanently Delete Items After 24 Days'

# Get existing retention tags linked to the retention policy
$taglinks = (Get-RetentionPolicy $retentionPolicy).RetentionPolicyTagLinks
# Add the new archive retention policy tag
$taglinks.Add($policyTag)
# Update the retention policy
Set-RetentionPolicy -Identity $retentionPolicy -RetentionPolicyTagLinks $taglinks

Depending on your organization and mailbox size, the Managed Folder Assistant may take a few minutes to several hours to process the mailboxes. Once the Managed Folder Assistant is finished running, the new retention policy will be available for users to select.

How to Verify Retention Policy Assignment and Processing?

After you assigned/modified an Exchange Online MRM retention policy, you should verify if the policy is assigned correctly and force the Managed Folder Assistant to process the mailbox immediately.

In order to check retention policy assigned to a mailbox, run the command:

Get-Mailbox -Identity user@domain.com | Select RetentionPolicy

Note that this command displays the retention policy currently assigned to the mailbox.

In order to force Managed Folder Assistant to process the mailbox, run the following command:

Start-ManagedFolderAssistant -Identity user@domain.com

The Managed Folder Assistant (MFA) processes Exchange retention tags asynchronously. This command forces immediate mailbox processing instead of waiting for the scheduled background cycle.

Note. This tutorial uses the Default MRM Policy. The retention policy name may be different in your environment. Make sure to specify the correct one.

Exchange Retention Policies and Litigation Hold

Keep in mind that Exchange Online MRM retention tags do not override Litigation Hold, eDiscovery Hold, Microsoft Purview retention policies, or other compliance retention mechanisms. In enterprise environments, mailbox items may remain preserved even after MRM retention actions are triggered.

For example, in case a mailbox is placed on Litigation Hold, items deleted by Exchange retention tags may still be preserved in the Recoverable Items folder for compliance and eDiscovery purposes.

Because of this behavior, “PermanentlyDelete” retention actions in Exchange MRM do not always mean that data is immediately and irreversibly removed from Microsoft 365.

In order to check whether Litigation Hold is enabled, run the command:

Get-Mailbox -Identity user@domain.com | Select LitigationHoldEnabled

The command above verifies whether the mailbox is protected by Litigation Hold.

In order to view mailbox hold-related settings, run the following command:

Get-Mailbox -Identity user@domain.com | Select LitigationHoldEnabled,RetentionHoldEnabled,InPlaceHolds

These properties help you to determine whether mailbox retention/compliance holds may prevent permanent item removal.

Conclusion

So, let’s assume that Exchange Online MRM remains useful for specific Exchange mailbox lifecycle cases, particularly automatic movement of messages to Online Archive and retention rules for specific Exchange default folders.

For new deployments, you should prefer Microsoft Purview over Exchange MRM. You need to use MRM only for mailbox-specific lifecycle management/when migrating from legacy Exchange configs.