TL; DR: Auto-Archiving for Exchange Online is being rolled out in October 2025 for all public clouds and in November for all government clouds. If archiving is already enabled for Exchange Online users, it automatically moves the oldest items from a user’s primary mailbox to their archive when the mailbox utilization approaches 90% of mailbox quota to help prevent mail flow disruptions.
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
Drawback of time-based archiving only
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 threshold 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 threshold-based 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 90% of mailbox quota, the system will start moving batches of the oldest items to archive mailbox until mailbox utilization drops below 90% 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). Time-based archiving will target the oldest emails first, moving them into the archive until the primary mailbox usage is safely below the threshold. This threshold-based archiving approach ensures that mailbox usage is brought back below the 90% 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 90% 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 near their quota. SLA of running Managed Folder Assistant on a given mailbox is 7 days.
Note: Oldest items in IPM folders are based on received date.
Availability
General Availability: starting October 15, 2025 in our WW cloud.
FAQs
Q: When will Auto-Archiving get triggered?
A: It will get triggered when user’s primary mailbox has exceeded 90% 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 90% 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 threshold-based Auto-Archiving will skip items/folders with “Never Move to Archive” tag.
Q: Which itemClasses are supported for Auto-Archiving?
A: All the ItemClass are supported for Auto-Archiving except "IPM.Appointment", "IPM.AppointmentSeries", "IPM.Task", "IPM.Contact", "IPM.DistList", "IPM.File", "IPM.File.Document".
Q: Will mailbox users notice that something has changed?
A: If their mailbox quota reaches 90%, 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.
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 to the archive mailbox. 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 90%, 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).
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. To prevent mail flow disruptions when a mailbox is critically full, Auto-Archiving will still be allowed to proceed even if Retention Hold is present on the mailbox which suspends Tag based archiving, while still respecting items with “Never move to Archive” tag. Moving items to the archive doesn’t break compliance—content remains preserved; no data is deleted by this feature.
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 90%.
Q: Is it possible to disable Auto-Archiving per mailbox or per tenant?
A: Disabling threshold-based Auto -Archiving is not possible because it is a failsafe mechanism to prevent any mail flow disruptions and only gets triggered when mailbox utilization crosses 90% (Critical) threshold and archiving is already enabled.
Aniket Gupta, Victor Legat and Exchange Online Archiving Team
