Exchange Online MRM Retention Policies: Archive Moves, Tags and Troubleshooting

MRM or Purview: which one, and when?​

Microsoft's guidance is specific. MRM is the legacy mailbox lifecycle system. For proactive retention and deletion across Microsoft 365, Microsoft recommends Purview retention policies and retention labels. Microsoft also says to keep using MRM when you need to move messages to archive mailboxes. The older feature keeps working side by side with Purview retention.

So MRM is not dead, and it isn't a full substitute for Purview either. It remains the tool for automatic archive moves.

The four moving parts​

The chain runs as follows:

1. Retention tags define an age and an action.
2. A retention policy bundles tags together.
3. The mailbox receives one policy. A mailbox can't have more than one MRM retention policy.
4. The Managed Folder Assistant (MFA) inspects items and acts on them.

Microsoft states that tags aren't applied to a mailbox until they're linked to a policy and the Managed Folder Assistant processes the mailbox. Assigning a policy therefore changes configuration, not content. Nothing moves until the assistant runs.

Three tag types, three scopes​

Default policy tags (DPTs) cover items that have no directly assigned tag and no inherited folder tag. A policy can hold one DPT that moves items to the archive. It can also hold one DPT that deletes items, plus a separate DPT for voicemail deletion.

Retention policy tags (RPTs) apply to supported default folders such as Deleted Items. They support only deletion actions, not Move to Archive. A policy can have one RPT per supported default folder.

Personal tags are options an administrator provides and users apply to individual items or folders. They can move to archive, delete with recovery, or permanently delete. In Outlook, personal tags with the Move to Archive action appear as Archive Policy. The delete variants appear as Retention Policy.

Microsoft says messages with a personal tag are always processed according to that tag's settings. That is why two messages of the same age in the same folder can end up with different outcomes.

What the Default MRM Policy actually does​

Exchange creates the Default MRM Policy and applies it automatically to new Exchange Online users. Microsoft's documented defaults include:

Two corrections to common assumptions follow from this.

• The default policy does not auto-delete Deleted Items. Microsoft says it includes no default tag for that folder. If you want a 30-day or custom period, you must add a suitable Deleted Items tag to the policy.
• The policy has no deletion DPT. The 730-day tag is a move, not a delete. It does include personal deletion tags, but users have to apply them.

You can edit the policy's tags, disable them, or add and remove them. You can't designate a different policy as the default for new users. Changes reach mailboxes the next time the MFA processes them.

Archive plus delete: how the pair is meant to work​

A policy can combine an archive DPT and a deletion DPT. Microsoft's planning rule is that the archive DPT must have a lower retention age than the deletion DPT. Its example moves items to the archive at two years and deletes them at seven. Retention settings extend to the online archive, so items are deleted after seven years from both primary and archive mailboxes.

Microsoft also says a DPT and personal tags can be combined to move items, and a DPT, RPTs and personal tags to delete items.

Be careful with precedence in mixed setups. A common scenario is a 730-day archive DPT with a user-applied five-year deletion tag. Microsoft says explicitly tagged items follow their own tag over folder or default tags. Microsoft's troubleshooting guidance adds that the tag with the longest duration, such as never move or never delete, takes precedence over other applied tags. Don't assume an item will archive at 730 days and then delete at five years. Test the combination on a pilot mailbox before promising users a behavior.

Moving an item also changes its tags. An item moved to another folder inherits that folder's tag. If the destination has no tag, the DPT applies. An explicit item tag still wins.

How retention age is calculated​

For ordinary email, age counts from the delivery date. For items created rather than delivered, such as drafts, it counts from creation. When the MFA processes items, it stamps a start date and an expiration date on items with delete-type tags. Archive-tagged items also get a move date.

Some item types behave differently:

• Calendar items: non-recurring items expire by end date. Recurring items with no end date don't expire.
• Contacts: not stamped, so they're skipped and never expire.
• Corrupted items: skipped and never expire.
• Deleted Items quirk: if an item sat in a folder with no inherited or implicit tag and is first processed in Deleted Items, the processing date becomes its start date. A 30-day Deleted Items rule then counts from that date, not from delivery.

Timing: why nothing seems to happen​

In Exchange Online, new retention settings can take up to seven days to apply, because the MFA processes mailboxes at least once every seven days. Microsoft notes this can leave items expiring up to seven days after their stamped date. Microsoft's troubleshooting page adds that the MFA usually runs more often, but a pass can take up to seven days to finish.

To request processing for one mailbox:

Start-ManagedFolderAssistant -Identity "<Mailbox Identity>"

This queues the work. It doesn't guarantee everything finishes while you watch. Microsoft's verification procedure is to run it, then sign in with Outlook or Outlook on the web and confirm that messages moved or were deleted as configured.

Inspecting your setup​

These Exchange Online PowerShell commands help you check what's configured:

Get-RetentionPolicy
(Get-RetentionPolicy "Default MRM Policy").RetentionPolicyTagLinks
Get-RetentionPolicyTag | Format-Table Name,Type,AgeLimitForRetention,RetentionAction
Get-Mailbox <MailboxID> | fl *Retention*

The last command shows the mailbox's assigned policy and its RetentionHoldEnabled value.

Troubleshooting checklist​

Microsoft's troubleshooting guidance lists these common reasons MRM doesn't act as expected:

• Retention hold: RetentionHoldEnabled is True, for example after a PST import migration.
• ElcProcessingDisabled is True: this stops the MFA from processing the mailbox at all.
• A disabled tag: items carrying it are never archived or deleted. Because they still count as tagged, the DPT doesn't apply to them.
• Large mailboxes: processing runs slower.
• Policies with only personal tags: if users don't apply them, little happens.
• Small mailboxes: MRM doesn't process mailboxes smaller than 10 MB.
• Disabled accounts: a disabled account with a regular mailbox isn't processed.

Further steps from Microsoft's guidance:

1. Check folder statistics, including the DeletePolicy and RetentionFlags columns. Compare the oldest item's received date against the tag's retention age.
2. Review MRM diagnostic logs with Export-MailboxDiagnosticLogs <mailboxID> -ComponentName MRM.
3. "Resource unhealthy" messages indicate throttling. Large mailboxes get processed slowly, and Microsoft calls this unavoidable.
4. Don't let the Recoverable Items folder hit its quota. That can also block moves into the archive.

Deletion, holds and what "gone" means​

Delete and Allow Recovery and Permanently Delete are different actions. The first lets users recover items until the deleted-item retention period ends. The second asks for permanent removal. Microsoft warns that while items are under Microsoft 365 retention policies, retention labels or litigation hold, they won't be permanently deleted and still show up in eDiscovery searches.

Don't treat retention hold as a legal hold.

• RetentionHoldEnabled: this pauses MRM processing, for cases like vacation. Microsoft says the MFA still applies tags but doesn't expire or archive items in user-visible folders. It does keep processing Recoverable Items. During the hold, users can change or delete items freely. Microsoft says you need a legal hold to preserve those changes.
• ElcProcessingDisabled: this is stricter. It stops all MFA processing for the mailbox, including expiring Recoverable Items. It can be set organization-wide. A locked Microsoft 365 retention policy overrides it.

Hybrid environments have one more trap. Microsoft says tags and policies must match on-premises and in Exchange Online for consistent behavior. A retention hold set in Microsoft 365 can also leave the on-premises MFA skipping purges in DiscoveryHolds. That can eventually fill Recoverable Items.

Bottom line​

A retention policy isn't a countdown timer. It's a menu of tags, and the tag that applies to each item sets its age and action. The Managed Folder Assistant does the work on its own schedule, which can take a week. Before blaming Exchange, check these in order:

1. the assigned policy
2. whether each linked tag is enabled
3. item- and folder-level tags
4. retention hold and ElcProcessingDisabled
5. any Purview or litigation holds that keep deleted content in storage

For new retention requirements, plan on Purview. Keep MRM for archive moves.