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Archiving and Unlimited Archiving in Office 365

Updated: May 15

In Microsoft 365, archive mailboxes refer to the additional mailbox storage space provided to users.

The primary intent for using archive mailboxes is for users to move data that they no longer use currently to a secondary mailbox. This helps save storage costs associated with the primary mailboxes.

First, archiving is turned OFF by default and has to be turned ON by the administrator – for each mailbox individually. Once this is done, the archive appears to be a separate folder in the user’s view within Outlook or Outlook on the web.

The archive size isn’t unlimited by default- it is set to 100GB at the start. But the administrator can choose to enable “auto-expanding archiving”. Once this is in place, when that archive folder reaches a 90% threshold, Office 365 automatically adds additional space in another archive folder.

After the archive mailbox is enabled, up to 100 GB of additional storage is available per user. Once the limit is reached, users can use a feature called auto-expanding archiving (also called unlimited archiving) that provides extra storage in the archive without contacting Microsoft. However, there is a limit of 1.5 TB to the auto-expanded archive.

Archive mailboxes act as secondary mailboxes that can be used to save on storage costs for mailbox items that are no longer actively used.

 Enabling Archive Mailboxes:

Access the Microsoft 365 admin center

Sign in to your Microsoft 365 admin account and navigate the admin centre.

Navigate to Users > Users

Within the admin centre, locate the Users section and click on Users. This will display a list of all users within your organization.

Select the mailbox you want to enable Archiving

From the list of users, identify the mailbox where you want to activate archive functionality. Click on the username to open their mailbox settings.

Click on Mailboxes settings

Once you've selected the user, locate the Mailbox settings option and click on it. This will open a detailed configuration panel for that specific mailbox.

Under Archive mailbox, toggle the switch to On

Within the Mailbox settings, scroll down to the Archive mailbox section. Here, you will find a toggle switch labelled On/Off. Click the switch to turn it On, enabling the archive mailbox functionality for this user.

Save the changes

After enabling the archive mailbox, click the Save button at the bottom of the settings panel. This will confirm the configuration changes for that user.

License Requirement

Archive mailboxes are available to all organizations that have an Exchange Online license.

Feature Access

Archive mailbox settings are available under 'MRM',


The archive mailbox has to be enabled to use this feature. Once enabled, admins and users can set it up to automatically move old messages to the archive.


Archive mailboxes can only archive emails for a single user or entity (such as a shared mailbox) for which a license has been applied. Using archive mailboxes for storing mail from multiple users or entities is not allowed.

Storage quota

After the archive mailbox is enabled, up to 100 GB of additional storage is available per user. Once the limit is reached, Microsoft provides an unlimited archiving feature where an extended archive gets added. However, the maximum limit after unlimited archiving is enabled is 1.5 TB per mailbox.

Level of application (item-level/container-level)

Specific mail, folders, or an entire mailbox can be archived.

Time for activation

The Managed Folder Assistant (MFA) periodically reviews items placed on retention and moves them to the archive mailbox if opted for.


Content in the archive, if deleted, is permanently lost. However, if the auto-expanding feature is enabled, items cannot be deleted from the archive mailbox.

Auto Expand Archive

An Auto-Expanding Archive provides more Archive storage space if needed. Default Archives have 100 GB of storage available. We must have additional storage if the archive is already over 100 GB.

Usually, a user gets 100 GB of storage for archiving; when a mailbox capacity is reached, auto-expanding will automatically add additional storage. Office 365 automatically adds storage space to the archive when necessary; another important point is that auto-expanding adds extra space for shared mailboxes as well.

Manage mailbox archive

Once you turn on auto-expanding archiving for your mailbox, it can take up to 60 days to get the additional storage. BTW, almost to state – you cannot turn off auto-expanding as soon as you turn on it.

Before you turn on “Auto-Expanding,” ensure you have enabled the archiving option for the user.

auto expanding archiving in M365

Once you turn on auto-expanding archiving for your mailbox, it can take up to 60 days to get the additional storage. BTW, almost forgot to state – you cannot turn off auto-expanding as soon as you turn on it.

Before you turn on “Auto-Expanding,” ensure you have enabled the archiving option for the user.

Enabling Auto-Expanding Archiving

(Note: Enabling auto-expanding archiving requires using Exchange Online PowerShell)

Connect to Exchange Online PowerShell

Open the Windows PowerShell application on your administrator machine. Run the following command to establish a connection to Exchange Online PowerShell.

connect exchange to online powershell

(This step might require additional authentication prompts. Follow the on-screen instructions to provide your credentials)

Identify the user mailbox:  

Once connected to Exchange Online PowerShell, run the following command to retrieve the user's mailbox identity (replace <username> with the actual username):

Archive mailbox steps

The output of this command will display various mailbox details, including the user's mailbox identity. Locate the property named Identity and copy the corresponding value.

Enable auto-expanding archive

Using the mailbox identity obtained in the previous step, run the following command to enable auto-expanding archiving for that user:

Auto expanding archive

(Replace <user_mailbox_identity> with the actual value you copied in the last step)

Verify the configuration

Run the following command once again to confirm that auto-expanding archiving is enabled for the user:

auto-expanding of archiving mailbox

Check the output for the property named AutoExpandingArchive. If its value is set to True, then auto-expanding archiving is successfully enabled for that user.

Benefits of Auto-Expanding Archiving

While traditional archive mailboxes offer a static storage increase, typically up to 100 GB, auto-expanding archiving provides several advantages:

Automatic Storage Growth

Auto-expanding archiving automatically increases the archive mailbox storage capacity as needed. This eliminates manual intervention to adjust storage quotas or monitor mailbox usage. It provides a "set it and forget it" approach for mailbox storage, ensuring users have ample email space.

Reduced Administrative Burden

For IT administrators, auto-expanding archiving simplifies mailbox management. Administrators can focus on other critical IT tasks without the need to constantly monitor storage usage and adjust quotas for individual users.

Peace of Mind for Users

Auto-expanding archiving offers users peace of mind regarding storage limitations. They can archive emails without worrying about exceeding mailbox quotas or encountering storage warnings. This fosters a more efficient workflow as users don't need to constantly delete emails to free up space.

Scalability for Growing Needs

Organizations with ever-increasing email storage demands benefit greatly from auto-expanding archiving. As email volumes grow, the archive mailbox automatically scales to accommodate additional storage needs, ensuring users have the required space.

Cost Optimization (Potential)

While storage consumption impacts your organization's Office 365 bill, auto-expanding archiving can optimize costs in some scenarios. Automatically expanding storage only as needed can be more cost-effective than pre-provisioning a large static storage quota for all users, which might not be fully utilized by everyone. However, monitoring overall storage consumption and implementing email retention policies is crucial to avoid unnecessary storage costs.

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1 Comment

Rizwan Ranjha
Rizwan Ranjha
Aug 31, 2023

Hi, You can use the blog below to find PowerShell help for this.

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