Microsoft Exchange Online: Auto-Archiving

Effective November 15, 2025, Exchange Online begins public preview of a new auto-archiving feature that automatically moves the oldest emails to an archive once a mailbox reaches 96% of its storage quota. This proactive cleanup works alongside existing time-based archiving to prevent mailboxes from hitting their limits (for example, due to large attachments or content generated by Artificial Intelligence (AI)). The feature is currently in a private test with select customers and is on track to be generally available to all Exchange Online users in January 2026.

What is Exchange Online Auto-Archiving

Exchange Online Auto-Archiving is an automatic mailbox management feature. It monitors mailbox storage and, when usage exceeds 96% of the quota, it moves the oldest email items from the primary mailbox to the archive mailbox. This process happens automatically and only transfers older emails (it does not delete them). By moving aging messages to the archive, the feature ensures the primary inbox has space for new emails. This complements the existing time-based email retention (which archives items after a set time period) by adding a capacity-based safety net. Auto-Archiving steps in before the mailbox becomes completely full, so users won’t lose the ability to send or receive email due to a maxed-out mailbox.

Key Features

• Automatic Trigger at 96%: The system continuously watches each mailbox’s usage. When a mailbox reaches 96% of its storage capacity, the auto-archive process kicks in. This threshold acts as a buffer to prevent hitting 100% which would stop incoming/outgoing mail.
• Oldest Emails Moved First: The feature targets the oldest messages in the mailbox first. Those emails are moved into the user’s Online Archive mailbox while keeping the same folder structure for easy reference. Emails remain accessible and searchable in the archive, just no longer counting against the primary mailbox quota.
• Avoids Email Disruption: By freeing up space automatically, it prevents email flow interruptions. Users are less likely to encounter bounced messages or an inability to send emails due to a full mailbox. This is especially helpful if a mailbox fills up quickly from big attachments or surges of AI-generated content.
• Works with Time-Based Archiving: The new Auto-Archiving feature complements existing archiving policies. It doesn’t replace your standard retention settings (e.g. “move to archive after 2 years”) but adds an extra layer of protection. If your mailbox grows too fast (before the time-based policy moves items), Auto-Archiving will step in to move items and protect your mailbox from overfilling.
• Transparent to Users: The auto-archiving happens in the background. Aside from noticing older emails now appearing in the Archive mailbox area, users do not need to take any action. All migrated emails stay in the archive with their original folder organization, and everything remains fully searchable and available in Outlook as usual.

Licensing

The Auto-Archiving feature is included as part of the Exchange Online service and uses the existing archive mailbox provided with your plan.

• Exchange Online Plan 1 includes a 50 GB archive mailbox.
• Exchange Online Plan 2 includes a 100 GB archive mailbox.

These archive size limits remain unchanged with the new feature – Auto-Archiving simply helps you make the best use of that space. There is no separate license needed specifically for Auto-Archiving; it will automatically work for any mailbox that has an archive enabled (under an eligible Exchange Online plan). For any detailed licensing questions or complex scenarios, it is recommended to seek expert advice from SCHNEIDER IT MANAGEMENT to ensure you have the right setup for your organization.

Frequently Asked Questions (FAQ)

Does Auto-Archiving require an archive mailbox to be provisioned?

Yes. Auto-Archiving only works if an archive mailbox is already enabled for the user. It does not automatically create archive mailboxes.

What happens if the archive mailbox is full?

If the archive mailbox is full and auto-expanding archives are not enabled, Auto-Archiving cannot move items. This may result in mail flow disruption. We recommend enabling auto-expanding archives for users to avoid this scenario.

Will Auto-Archiving override existing retention or deletion policies?

No. Auto-Archiving does not change deletion or retention policies. It only relocates items to the archive to prevent mailbox quota lockouts.

Can Auto-Archiving be disabled for specific mailboxes or the entire tenant?

Yes. Administrators can disable Auto-Archiving per mailbox using PowerShell:

Set-Mailbox <user-smtp-address> -AutoArchivingEnabled $false

To adjust or disable the threshold organization-wide, use:

Set-OrganizationConfig –AutoArchivingThresholdPercentage <value>

Valid range: 80–100 (Default: 96). Setting the threshold to 100 disables Auto-Archiving tenant-wide.

How can administrators monitor Auto-Archiving activity?

Detailed diagnostics are available via Exchange Online PowerShell:

Export-MailboxDiagnosticLogs -Identity <user> -ComponentName MRM

Logs include item counts, total bytes archived, and trigger details for auditing and transparency.

Will Auto-Archiving respect “Never Move to Archive” tags?

Yes. Items or folders tagged with “Never Move to Archive” will not be moved.

Does Auto-Archiving work if ELC (Exchange Lifecycle) processing is disabled?

No. Auto-Archiving requires ELC processing to be enabled on the mailbox.

More Information

For more details and frequently asked questions about this new feature, please refer to the official announcement and FAQ: https://techcommunity.microsoft.com/blog/exchange/auto-archiving-for-exchange-online/4459735.

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