Learn about auto-expanding archive - Microsoft Purview (Compliance) (2023)

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Archive mailboxes in Microsoft Purview provide users with additional mailbox storage space. Once a user's archive mailbox is activated, up to 100 GB of additional storage is available.

This archiving feature in Microsoft Purview (calledauto-expanding file) provides up to 1.5 TB of additional storage space in archive mailboxes. When the archive mailbox storage quota is reached, Microsoft Purview automatically (and incrementally) increases the archive size until the archive mailbox reaches 1.5 TB.

For step-by-step instructions on how to enable auto-expanding archiving, seeEnable auto-expand file.


Auto-expanding archiving also supports shared mailboxes.


If you're not an E5 customer, you can try all the premium features of Microsoft Purview for free. Use the Purview Solutions 90-day trial to learn how Purview's robust features can help your organization meet data security and compliance requirements. Restart nowMicrosoft Purview Compliance Portal Test Center🇧🇷 Know details aboutRegistration and evaluation conditions.

This is how the auto expand file works

As explained in the introduction, additional mailbox space is created when a user's archive mailbox is activated. When auto-expanding archiving is enabled, Microsoft Purview periodically checks the size of the archive mailbox. When an archive mailbox reaches its storage limit, additional storage space is automatically created for the archive. When the user runs out of extra space, more space is automatically added to the user's file. This process continues until the user file reaches a size of 1.5 TB. This process is automatic, which means that administrators do not need to request additional file storage or manage auto-expanding files.

Here is a brief description of the process.

Learn about auto-expanding archive - Microsoft Purview (Compliance) (1)

  1. Archiving is enabled for a user mailbox or a shared mailbox. An archive mailbox with 100 GB of storage space is created, and the archive mailbox warning quota is set to 90 GB.

  2. An administrator enables auto-expanding archiving for the mailbox. If the mailbox has a hold or lock policy applied, the archive mailbox storage quota increases to 110 GB and the archive alert quota increases to 100 GB.

    Then, when the archive mailbox (including the Recoverable Items folder) reaches its storage quota, the archive mailbox is converted to an auto-expanding archive. Additional storage is added up to a maximum size of 1.5TB. It may take up to 30 days for additional storage to be provided.

  3. Microsoft Purview automatically adds more storage space as needed.


Auto-expanding archiving is only supported for mailboxes used by individual users (or shared mailboxes) with a growth rate of no more than 1 GB per day. A user's archive mailbox is for that user only. Using journaling, transport rules, or automatic forwarding rules to copy messages to an archive mailbox is not allowed. Microsoft reserves the right to refuse additional archiving in cases where a user's archive mailbox is used to store archive data for other users or in other cases of inappropriate use.

What moves to additional file space?

Folders can be moved to make efficient use of automatically expanding file memory. Microsoft Purview determines which folders are moved when additional space is added to the file. Sometimes moving a folder automatically creates one or more subfolders and distributes items from the original folder to those folders to simplify the move process. It may be necessary to communicate this behavior to end users after enabling their mailboxes so that the files automatically expand to meet expectations.

When you view the file portion of the folder list in Outlook, these subfolders appear below the original folder. The naming convention that Microsoft 365 uses to name these subfolders is<folder name>_yyyy (Created on dd mmm, yyyy h_mm), Wo:

  • aaaaaais the year that the messages in the folder were received.

  • mmm tt, aaaa h_mis the date and time the Office 365 subfolder was created, in UTC format, based on the user's time zone and regional settings in Outlook.

The screenshots below show a list of folders before and after messages are moved to an auto-expanding file.

Before adding additional memory

Learn about auto-expanding archive - Microsoft Purview (Compliance) (2)

After adding additional memory

Learn about auto-expanding archive - Microsoft Purview (Compliance) (3)


As described above, Microsoft Purview moves items into subfolders (and names them using the naming convention described above) to help distribute content to a sidecar file. However, moving items to subfolders is not always the case. Sometimes an entire folder can be moved to a sidecar file. In this case, the folder keeps its original name. The Outlook folder list does not indicate that the folder has been moved to a sidecar file.

Outlook requirements to access items in an auto-expanding file

To access messages stored in an auto-expanding file, users must use one of the following Outlook clients:

  • Outlook as part of Microsoft 365 Apps for enterprise (formerly known as Office 365 ProPlus)

  • Outlook as part of Microsoft 365 Apps for enterprise (formerly called Office 365 Business)

  • Outlook 2016 or Outlook 2019 for Windows

  • Outlook on the web when the primary mailbox is in Exchange Online instead of on-premises

  • Outlook 2016 or Outlook 2019 for Mac

Here are some things to consider before enabling an auto-expanding mailbox:

  • Users can access all folders in their archive mailbox, including those that have been moved to the auto-expanding storage area.

  • If an archive mailbox has at least one auto-expanded extension, users cannot delete an archive mailbox or auxiliary file folder. In other words, you can no longer exclude folders from the archive after provisioning an auto-expanding storage area.

  • Users can delete items in an auto-expanding storage area. However, you cannot use them.Function to recover deleted itemsto retrieve an item after auto-expanding archiving has been enabled for your mailbox.

  • Advanced automatic file search is available in Outlook for the web (OWA). Similar to the online archive, users can search for objects that have been moved to an additional storage area. When File is selected as the search scope in OWA, all files (including self-expanding files) and their corresponding subfolders are searched.

  • Automatic file search is available if you're using Outlook for Windows on the monthly retail channel, version 16.0.13519+. With this update, the current mailbox panel is available, allowing users to automatically search the improved archive. However, the search is not recursive for nested subfolders within each file folder.

  • Search does not support the auto-expanding archive feature in a cloud-only archive scenario (the primary mailbox is still on-premises). For more information about this and other Microsoft Search support resources, seeHow Outlook for Windows connected to Exchange Online uses Microsoft Search.

  • The number of items in Outlook and the number of read/unread items (in Outlook and Outlook on the web) in an auto-expanding file may not be accurate.

File auto-expanding and other compliance features

This section explains the functionality between auto-expanding archiving and other compliance features.

  • electronic discovery:When you use an eDiscovery tool such as content search, it also looks for additional storage areas in an auto-expanding file.

  • retention:When you archive a mailbox using methods such as Microsoft 365 Hold, eDiscovery case hold, and Litigation Hold in Exchange Online, the content is also archived in an auto-expanding archive.

  • Message recording management (MRM):If you use MRM deletion policies in Exchange Online to permanently delete expired mailbox items, any expired items that are in the auto-expand file are also deleted.

Next steps

For more technical details on the auto-expand file, seeMicrosoft 365: Automatic file expansion FAQ.

If you're ready to enable auto-expanding archiving, keep readingEnable auto-expand file.


How does auto-expanding archive work? ›

When auto-expanding archiving is turned on, additional storage space is automatically added to a user's archive mailbox until it reaches the storage limit of 1.5 TB. You can turn on auto-expanding archiving for everyone in your organization or just for specific users.

Does E3 include archiving? ›

Customers with Microsoft Office 365 E3 licenses and above are essentially led to believe they have an unlimited mailbox size. In reality, they have a mailbox that can be set to a maximum of 100GB, and an unlimited amount of space for archive email. It is important to understand how archiving with Office 365 works.

What does personal 1 year move to archive mean? ›

Retention Policy Tag (Deleted Items); this tag is automatically applied to items in the Deleted items folder. Personal 1 year move to archive. Moves items to the archive mailbox after 1 year. Built-in. Personal; this tag can be applied by users.

Does AutoArchive delete emails? ›

AutoArchive is a feature in Outlook that moves old mail and other items to a separate personal folder ( . pst ) file on your computer's hard drive, or a workgroup or departmental server. By default, it will prompt you before archiving items every 14 days and delete expired email messages from your mailbox.

How to check if auto expanding archive is enabled for a user? ›

In the Exchange Admin Center (EAC), open the info pane of the user's mailbox. Click on “Manage mailbox archive”. An Auto-Expanding Archive provisions more Archive storage space, if needed. Default Archives have 100 GB of storage available.

Does Auto archive keep folder structure? ›

Your existing folder structure is maintained in your new archive file. If there is a parent folder above the folder that you archived, the parent folder is created in the archive file. But the items that are in the parent folder are not archived.

Can you have different AutoArchive settings for different folders in your mailbox? ›

To specify unique settings for one or more folders, do not choose this option. Instead, right-click the folder, click Properties and then go to the AutoArchive tab to change settings for each folder that you want to change.

What are the 2 main archiving types? ›

What are the 2 types of archiving? There are two main types of archives: paper and digital. In a paper archive, documents are stored in the order they were created and in a digital archive they are stored in chronological order.

What's the difference between archive and in place archive? ›

The key difference between the older AutoArchive feature and in-place archives is simple: AutoArchive automatically moves old emails to off-server PST files. Since the emails are in PST files, they are harder for users to search and don't offer the same convenience and agility of in-place archives.

Does Office 365 F3 include archiving? ›

Max mailbox size in Microsoft 365

An F3 (Kiosk) license includes only 2 GB of storage and it doesn't provide archive mailboxes.

How long do documents stay in archive? ›

Accounting document retention policy As a general rule of thumb, tax returns, financial statements and accounting records should be retained for a minimum of six years.

What is the difference between archive and PST? ›

Basically, all pst-files are equal; They store their data in the same way and can be reopened on other computers with Outlook. When a pst-file isn't directly associated with a mail account (POP3 or IMAP), we refer to them as archives.

What does the automated archive system do? ›

Automated Property System (APS) - APS maintains information regarding stolen, lost, found, under observation and evidence held property. The stolen bicycle file is a sub-file of APS.

Does auto archive free up space in Outlook? ›

AutoArchive takes the oldest items and moves them to a PST file on your hard drive to free up space in the mailbox. The AutoArchive feature can also help people without an Exchange server mailbox by making the main PST file smaller. The main PST file on their hard drive is saving their mail and other Outlook items.

Does auto archive reduce mailbox size? ›

Outlook Archive Does Not Reduce Mailbox Size – Quick Tricks to Fix Error. Almost all Outlook users may be familiar with the 'Outlook archive does not reduce mailbox size' issue. This error will occur when the PST file exceeds the recommended size and users must reduce the size of PST file using the archive option.

What happens when archive mailbox is full? ›

Then, when the archive mailbox (including the Recoverable Items folder) reaches its storage quota, the archive mailbox is converted to an auto-expanding archive. Extra storage space is added until it reaches a maximum size of 1.5 TB. It can take up to 30 days for the additional storage space to be provisioned.


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