Compliance Problems

Fix Microsoft 365 Retention Policy Not Moving Emails to Archive

Maira Mehtab Sep 21, 2026 869 views

Question details

A user's Microsoft 365 mailbox is not archiving older emails despite an active 2-year retention policy, and they are experiencing duplicate data issues after a PST migration.

Product: Microsoft 365
Device & OS: not provided
Scenario: Migrating PST files and applying a default 2-year move-to-archive retention policy to manage mailbox size.
Observed behavior: Older messages have not moved to the archive after approximately two weeks, leaving the mailbox nearly full. Additionally, duplicate emails, contacts, and calendar events appeared after the migration.

Before you start

Ensure the affected mailbox has a valid Exchange Online Archiving license assigned, as this is required for move-to-archive retention policies to function.

Solution 1Recommended

Contact Microsoft 365 Support for Backend Investigation

Since retention policy processing and mailbox synchronization require backend access to the Managed Folder Assistant, a Global Administrator must open a service request.

Community moderators and standard users do not have access to the backend logs required to diagnose why the Managed Folder Assistant is failing to process the mailbox archive policy. Microsoft Support can force the assistant to run, collect advanced logs, and investigate the duplicate data resulting from the PST migration.

Log in to the Admin Center

Access Help & Support

Navigate to the lower right corner or the left-hand menu and click on the 'Help & support' icon.

Open a Service Request

Describe the issue regarding the delayed retention policy and duplicate PST data, then follow the prompts to click 'Contact support' and open a formal service request.

Reseller Subscriptions: If your Microsoft 365 subscription was purchased through a third-party reseller (such as GoDaddy or AppRiver), you must contact the reseller directly for administrative and technical support.

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Frequently Asked Questions

Why is my Microsoft 365 retention policy taking so long to move emails?

The Managed Folder Assistant (MFA), which processes retention policies in Microsoft 365, runs on a regular work cycle. It can sometimes take up to 7 days to fully process a mailbox, especially if the mailbox is large, newly configured, or if there are backend throttling constraints.

Can I manually force the retention policy to run on a mailbox?

Yes, Exchange administrators can force the Managed Folder Assistant to process a specific mailbox by connecting to Exchange Online via PowerShell and running the command: Start-ManagedFolderAssistant -Identity <UserMailbox>.

How do I remove duplicate emails after a PST migration?

Microsoft 365 does not have a native backend deduplication tool. Users can use the 'Clean Up' tool in the Outlook desktop client (found on the Home tab) to remove redundant messages, or administrators may need to utilize third-party deduplication software for widespread issues.

Do I need a special license for Microsoft 365 archiving?

Yes, to utilize a 'move to archive' retention policy, the user must be assigned an Exchange Online Plan 2 license or an Exchange Online Plan 1 license combined with the Exchange Online Archiving add-on.

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