Exchange Online Retention: How MRM Policies and Tags Work

This article explains legacy Exchange Online Retention in the form of Messaging Records Management (MRM). Not the complete Microsoft Purview retention model. MRM can appear deceptively simple: create a policy, add retention tags, assign it to a mailbox, and wait for older messages to be deleted or moved to the Online Archive.

In practice, the policy is only the starting point. What happens to a message depends on the applicable tag, its retention age, its configured action, and mailbox processing.

Based on my years of working with these policies, the most useful way to understand retention is to separate the configuration from the processing. Assigning a policy tells Exchange Online which tags are available; it does not immediately move or delete the mailbox’s content.

This article focuses on Exchange Online Messaging Records Management (MRM): how policies and tags fit together, how they apply to messages and folders, and how the Managed Folder Assistant carries out the configured actions.

MRM versus Purview retention: Use MRM when you need to automatically move messages to archive mailboxes. For new proactive retention and deletion requirements, Microsoft recommends Microsoft Purview retention policies and retention labels. MRM remains supported and can coexist with Purview retention.

Another preservation requirement, such as a Purview retain setting or a legal hold, can prevent permanent deletion even after an MRM deletion action removes a message from a user-visible folder; the apparent deletion result is therefore not necessarily the final storage outcome.

The goal is to understand the lifecycle of a message, from the policy assigned to its mailbox to the action Exchange eventually takes.

How Exchange Online retention works with MRM

Messaging Records Management, or MRM, is Exchange’s traditional email lifecycle-management system. It uses retention tags and retention policies to determine when Exchange should move, delete, or permanently delete mailbox content.

An MRM implementation essentially has four components:

Retention tags → Retention policy → Mailbox → Managed Folder Assistant

Each component has a distinct role. Retention tags define the age and action. A retention policy groups those tags so they can be assigned to a mailbox. The mailbox contains the content to which the configuration applies. The Managed Folder Assistant evaluates that content and processes items according to their applicable tags.

A single policy can therefore offer several behaviors rather than one universal retention period. For example, an organization might configure:

• Move untagged messages to the archive after two years.
• Delete messages from Deleted Items after 30 days.
• Allow users to select a personal “Delete after 5 years” tag.

Microsoft’s Default MRM Policy provides several examples of these concepts. In Exchange Online, the Default MRM Policy is automatically assigned to new users and includes tags such as “Default 2 years move to archive” and several personal archive and deletion tags.

The three types of MRM retention tags

MRM uses three types of retention tags. Their scope—otherwise untagged items, default folders, or user-selected messages and folders—helps explain why a single mailbox can contain content with different retention behavior.

Default policy tags

A Default Policy Tag (DPT) supplies the default behavior for otherwise untagged mailbox items. It provides a baseline without requiring users to choose a tag for every message.

For example, a DPT might configure:

730 days → Move to Archive

With this archive DPT, messages without another applicable archive tag can move to the Online Archive when they reach the specified retention age. The tag defines both the threshold and the destination; the Managed Folder Assistant performs the move.

A retention policy can contain a DPT for deletion and another DPT for archiving. These actions serve different purposes: archiving moves content to the archive mailbox, while deletion determines when content is removed. Moving a message to the archive is not the same as deleting it.

Retention policy tags

Retention Policy Tags (RPTs) apply to specific default mailbox folders, such as Deleted Items.

A folder-specific tag lets a default folder follow a different deletion schedule from the rest of the mailbox. For example, a Deleted Items tag can define a shorter retention period for that folder while other content follows the applicable default or personal tag.

Personal tags

Personal tags give users some control over individual items or folders. Depending on how the tag is configured, users can assign a personal tag to messages or folders in Outlook.

An organization could provide personal options such as:

• Delete after 1 year.
• Delete after 5 years.
• Never delete.
• Move to archive after 1 year.

The containing folder does not always tell the whole story. A personal tag on an individual message can cause that message to follow a different schedule from other messages in the same folder. The mailbox policy supplies the available tags, but the applicable folder or item tag determines the behavior for that content.

What a retention policy actually does

A retention policy is a collection of retention tags, not a single mailbox-wide countdown. Its purpose is to bring the required default, folder-specific, and personal options together in a configuration that can be assigned to mailboxes.

The following PowerShell command lists the MRM retention policies configured in Exchange Online:

Get-RetentionPolicy

The mailbox’s RetentionPolicy property identifies its assigned MRM policy:

Get-Mailbox [email protected] | Format-List RetentionPolicy

The policy’s RetentionPolicyTagLinks property identifies the tags included in that policy:

(Get-RetentionPolicy "Default MRM Policy").RetentionPolicyTagLinks

The tag definitions describe the behavior behind those names:

Get-RetentionPolicyTag | Format-Table Name,Type,AgeLimitForRetention,RetentionAction

This displays several particularly useful properties:

• Name identifies the tag.
• Type identifies whether it is a default, folder-specific, or personal tag.
• AgeLimitForRetention determines the retention period.
• RetentionAction determines what happens when that age is reached.

Possible actions include moving an item to the archive, deleting it while allowing recovery, and permanently deleting it.

A policy name such as “Three Year Retention” is only a label. The linked tags define which content is affected, the retention period, and whether the action is archiving, deletion with recovery, or permanent deletion. Understanding the policy means understanding those definitions, not just its name.

The Managed Folder Assistant does the work

Assigning a retention policy doesn’t immediately cause Exchange Online to start moving or deleting messages.

The actual processing is performed by the Managed Folder Assistant (MFA).

The Managed Folder Assistant evaluates mailbox items and applies the appropriate retention actions. A change to the Default MRM Policy takes effect for a mailbox when the assistant next processes it. Configuration and execution are therefore separate stages of the same lifecycle.

Administrators can explicitly request mailbox processing with:

Start-ManagedFolderAssistant -Identity [email protected]

This command requests processing; it does not synchronously process every item while the PowerShell session waits. A heavily populated mailbox should not be expected to change instantly.

The same distinction applies whether a policy was just assigned or a tag was changed: the configuration describes the intended behavior, and the assistant carries it out during mailbox processing.

Think about MRM as a pipeline:

Policy assigned → Tags evaluated → Retention age calculated → Managed Folder Assistant processes mailbox → Retention action occurs

This sequence explains why a policy assignment alone does not establish that a message has already been moved or deleted. The applicable tag, retention age, and processing all contribute to the result.

Retention age and the applicable tag

A retention period answers “when,” while the retention action answers “what happens.” A tag configured to move content to the archive after two years is different from a tag configured to delete content after two years, even though the periods are the same.

The applicable tag is equally important. Otherwise, untagged content can follow a default policy tag, content in a default folder can follow a folder-specific tag, and a user-selected personal tag can give a message a different schedule. Two messages of the same age can therefore receive different treatment within the same mailbox.

It helps to think of retention as a rule applied to content, rather than a blanket promise that everything older than a particular date will disappear. Exchange evaluates the content against the applicable tag and its retention age before carrying out the configured action.

One mailbox, one message: A mailbox with an enabled Online Archive is assigned an MRM policy containing a default tag that moves otherwise untagged messages to the archive after 730 days. A user applies a personal five-year deletion tag to one message. That message’s deletion schedule is five years, not 730 days; a deletion tag should not be read as an instruction to postpone archiving. When the Managed Folder Assistant processes the mailbox, Exchange evaluates the applicable tags and the message’s retention age rather than treating the policy name as a mailbox-wide rule. The message can become eligible for the archive move at 730 days and for its personal deletion action at five years, including after it has moved to the archive. A separate preservation requirement can still prevent permanent removal.

Archiving, deletion, and holds are different concepts

An archive action moves messages to the Online Archive rather than deleting them. The archive mailbox is therefore part of the retention lifecycle when a tag uses MoveToArchive. A message no longer visible in the primary mailbox may still be available in the archive.

Deletion has its own lifecycle. Depending on the retention action and mailbox configuration, deleted content can move through Recoverable Items. Removal from a user-visible folder does not necessarily mean immediate physical removal from Exchange Online, and the visible folders do not represent all stored mailbox data.

Holds also affect the outcome. RetentionHoldEnabled can prevent normal MRM processing from behaving as expected, while other retention or hold mechanisms can affect deletion. These settings are part of the mailbox’s broader retention context; they should not be treated as interchangeable with the age and action defined by an MRM tag.

Putting the retention lifecycle together

Exchange Online MRM is best understood as a set of connected responsibilities. The policy groups the tags. The applicable tag defines the retention period and action. The Managed Folder Assistant evaluates and processes the content. Archive availability, holds, and Recoverable Items help determine what users and administrators ultimately see.

That is the central distinction: a retention policy defines the configuration, but it is not the action itself. Understanding how the components fit together makes it easier to explain why messages in one mailbox can follow different schedules—and why archiving, deletion, and permanent removal are not the same event.

Frequently asked questions