Update 10/17/2025: We updated the content of this blog post, the timelines and the FAQ to align with customer feedback we received after initial announcement.
TL; DR: A new capability called Auto Archiving for Exchange Online will enter public preview from November 15, 2025 (currently under private preview for selected customers). When a user's mailbox utilization exceeds 96% of its quota and archive mailbox is present, this feature automatically moves the oldest items excluding those tagged with “Never Move to Archive” from the primary mailbox to the archive mailbox to prevent mail flow disruptions by keeping usage below the safe threshold of 96% of mailbox quota.
The need for archiving
Users archive their primary Exchange Online mailboxes to avoid hitting mailbox storage limits, ensure uninterrupted email access, and maintain a clean and organized inbox while still retaining older messages for reference. Archiving also supports compliance with regulatory and legal retention requirements enabling seamless access to historical data through archive views in Outlook
Limitations of tag-based archiving (current behavior)
Even when users configure MRM policies like “Move to Archive after 2 years,” they still may encounter mailbox quota full issues because the volume of incoming data especially from large attachments, automated notifications, and AI-generated content (Copilot generated meeting notes, automated/system generated reports) often exceeds expectations. Users assume that archiving will proactively manage mailbox size, but the archive only activates after a fixed age is met. This could allow data to accumulate rapidly and unexpectedly. As a result, mailboxes can reach full capacity before time-based archiving kicks in, leading to functional loss such as inability to send or receive emails directly impacting business continuity and operational efficiency.
Reimagining archiving: adding Auto Archiving to time-based archiving
Responding to requests of customers who emphasized the need for proactive and automated space management that complements existing retention settings, we are rolling out an update designed to prevent mail flow disruption due to misconfigured archiving policies or situations where mailboxes might fill up faster than expected. With this design change, when mailbox utilization exceeds 96% of mailbox quota, the system will start moving batches of the oldest items to archive mailbox until mailbox utilization drops below 96% utilization in both IPM (visible to users) and recoverable items folders (that if archive mailbox is provisioned for the user and has storage capacity remaining). Auto Archiving will target the oldest emails first, moving them into the archive until the primary mailbox usage is safely below the threshold. Auto archiving approach ensures that mailbox usage is brought back below the 96% threshold before users experience functional loss such as inability to send or receive emails ensuring real-time mailbox health monitoring across organizations.
Note: This feature is called Auto-Archiving which is different from Auto expanding Archive.
How it works
The Managed Folder Assistant will continuously monitor the primary mailbox size. As and when primary mailbox size exceeds 96% of the current mailbox quota and provided the archive mailbox is provisioned and has remaining space, Managed Folder Assistant will automatically archive the oldest items first until usage drops below the threshold. The same concept applies to Recoverable Items (“Dumpster”) folders when they are near their quota.
Note: Oldest items in IPM folders are based on received date.
Availability
- Public Preview: starting November 15, 2025, enabled for tenants who have opted into Targeted Release option.
- General Availability (WW cloud): January 15, 2026 (tentative)
- Government clouds roll out: February 15, 2026 (tentative)
We are creating a Microsoft 365 Roadmap item for this feature and plan to send a Message Center post to tenants who the feature will impact, before GA.
FAQs
Q: When will Auto-Archiving get triggered?
A: It will get triggered when user’s primary mailbox has exceeded 96% utilization, the archive mailbox is already provisioned and has remaining storage capacity for items to be archived.
Q: What will happen to our current archiving policy?
A: There is no change in how archiving policy works today. Auto Archiving will only kick in as failsafe once primary mailbox size exceeds 96% threshold of mailbox quota to avoid any mail flow disruptions. Once Auto Archiving gets triggered, it will temporarily override the current archiving policy and move batches of oldest items based on received date till mailbox utilization drops below the threshold.
Q: We have items/folders with the “Never Move to Archive” tag. What will happen to those items once Auto-Archiving kicks in?
A: The “Never Move to Archive” tag will be still honored. That means the Auto Archiving will skip items/folders with “Never Move to Archive” tag.
Q: Will mailbox users notice that something has changed?
A: If their mailbox quota reaches 96%, their oldest mailbox items will move to the “Online Archive –” tree while preserving folder structure; mail remains searchable and accessible.
Q: Will this feature also provision archive mailboxes on behalf of users?
A: No. Auto Archiving will only get triggered if the archive mailbox is already provisioned for the user and hence no Archive mailboxes are provisioned automatically on behalf of users unless they are explicitly enabled.
Q: Our user’s Main Archive is full, and auto-expanding archive is not enabled. Will this feature enable auto expansion of archives on behalf of the user?
A: No. This feature will not enable auto expansion of archives on behalf of the user. If the main archive is full, no items will be moved from primary to the main archive. This might result in mailboxes getting full, thus disrupting mail flow. It is advised that auto expansion is enabled for users manually to avoid this scenario.
Q: An archive mailbox has been provisioned for an account, but there is currently no default archiving policy enabled. Will emails be automatically archived when mailbox utilization exceeds 96%, ensuring the primary mailbox does not reach its storage limit?
A: Yes. With this feature, it is not necessary to implement an archiving policy for managing storage utilization in the primary mailbox if archiving has already been enabled (archive mailbox provisioned). But it is recommended to lower the threshold to 90% for the better experience.
Q: Does this change deletion/retention policies?
A: No. This feature doesn’t change deletion behavior; it only relocates items to the archive to prevent primary mailbox quota lockouts.
Q: A mailbox is under Retention hold. Will Auto Archiving still get triggered?
A: Yes. Auto Archiving will archive items even if Retention hold is enabled.
Q: How do we prevent specific important information from being archived?
A: We recommended to use “Never Move to Archive” Tag to prevent important information from being archived.
Q: Is it possible to get details of Auto-Archiving which automatically manages space for a mailbox?
A: Yes. Detailed diagnostics are published for transparency and auditing which can be accessed from Exchange Online shell for a given user.
Export-MailboxDiagnosticLogs -Identity $user -ComponentName MRM
Sample Log:
<Date>; method: PublishDiagnosticsLog; ... Auto- Archiving completed for mailbox: <MbxGuid>. Items archived till date: <Date>. Total items archived: <ItemCount>, Total bytes archived: <Size>. Auto-Archiving was triggered to move <xyz GB> of data because mailbox utilization crossed 96%.
Q: ELC processing is disabled for the mailbox. Will auto archiving still happen for the mailbox?
A: No. Auto archiving will only get triggered if ELC is enabled on the mailbox.
Q: Is it possible to disable Auto-Archiving per mailbox or per tenant?
A: If mailbox size is less than the Auto Archiving threshold percentage (default value is 96%), items will not be archived. Auto Archiving can be turned off for individual mailboxes using the following PowerShell command:
Set-Mailbox <user-smtp-address> -AutoArchivingEnabled $false
To adjust the threshold setting at the organization level, administrators can use the command below:
Set-OrganizationConfig –AutoArchivingThresholdPercentage 96
- Default Value: 96
- Valid Range: 80–100
If the Organization AutoArchivingThresholdPercentage is set to 100, Auto Archiving will not take place for the entire tenant.
Aniket Gupta, Victor Legat and Exchange Online Archiving Team
