Exchange Online

How to Export Mailbox Folder Size Report in Exchange Online

As emails and attachments pile up in Exchange Online, mailbox folders can grow quickly and push mailboxes closer to their storage limits. If the folder storage is left unchecked, it can lead to degraded performance, sync delays, and quota issues. To prevent such problems, it’s important to understand how storage is used across Exchange mailbox folders. This guide shows how to export the mailbox folder size report in Exchange Online and manage storage effectively.

Get Microsoft 365 Mailbox Folder Size Using PowerShell

Microsoft 365 Permission Required

View-Only Organization Management Least Privilege

Global Admin Most Privilege

Connect to the Exchange Online PowerShell using the cmdlet below.
Windows PowerShell
```
 Connect-ExchangeOnline
```
Run the below cmdlet to get the Exchange Online mailbox folder size report using PowerShell.

Windows PowerShell

 Get-Mailbox | ForEach-Object { 
Get-MailboxFolderStatistics $_.UserPrincipalName | 
Select @{Name='User';Expression={$_.Identity}}, Name, FolderSize, FolderPath, ItemsInFolder } | 
Export-Csv "C:\user\AllMailboxFolderSizes.csv" -NoTypeInformation

Get Microsoft 365 Mailbox Folder Size Using PowerShell

Track Mailbox Folder Statistics in Exchange Online Using PowerShell Script

Microsoft 365 Permission Required

View-Only Organization Management Least Privilege

Global Admin Most Privilege

As the default PowerShell cmdlet offers only limited insights into mailbox folder sizes, we’ve created a custom script that delivers a comprehensive report.
It captures detailed information, such as folder sizes, item counts (both visible and hidden), folder types, last modified timestamps, and more for all mailbox folders.
Download and run the script to get a complete, user-friendly breakdown of the mailbox folder storage report.
Windows PowerShell
```
 ./GetMailboxFolderStatisticsReport.ps1
```

Track Mailbox Folder Statistics in Exchange Online Using PowerShell Script

GetMailboxFolderStatisticsReport.ps1

Simple & Quick
Export Exchange Mailbox Folder Size Report Using AdminDroid

AdminDroid Permission Required Delegated

Any user with the report access delegated by the Super Admin

Login to the AdminDroid 365 portal.
Navigate to the All Mailbox Folders report under Reports»Exchange»Deep Insights»Folder Insights»All Folders.
Click the Download button to export the mailbox folders statistics report in various formats like CSV, XML, HTML, etc.
This report provides detailed insights into the size of each mailbox folder in Exchange Online. It includes key details such as mailbox folder size, total email counts, folder paths, folder type, subfolders count, and more.

Export Exchange Mailbox Folder Size Report Using AdminDroid

Admins must enable Exchange Online Deep Insights tracking for mailboxes to view the folder size report and their related details.

AdminDroid Exchange Online Reporter

Keep an Eye on Mailbox Folder Size Growth to Maintain a Clutter-free Exchange Online

AdminDroid's Exchange Online auditing tool provides deep insights into each folder across all user and shared mailboxes in your organization. It helps detect folder insights, streamline storage usage, and enable proactive mailbox management to avoid performance and quota issues. Below are a few insights that help you monitor Exchange Online mailbox folder activities and maintain overall mailbox hygiene.

Audit Mailbox Folder Permission for Unusual Access Changes

Audit mailbox folder permission changes in Exchange Online to track unauthorized access attempts and ensure only intended users have folder-level access.

Monitor Mailbox Folder Statistics to Manage Storage Better

Analyze mailbox folder statistics to understand how emails with attachments, sent emails and other email types contribute to folder size and take relevant action to free up space.

Manage Recoverable Items Folders to Prevent Mailbox Size Growth

Monitor recoverable items folder statistics to pinpoint deleted emails taking up space in hidden folders and remove unwanted ones to free up overall mailbox storage.

Trace Folder-Level Activity in Mailboxes for Better Oversight

Audit all Exchange Online mailbox folder events to catch every change across folders, ensure accountability, and maintain better control over mailbox usage.

Identify and Clean Up Idle Exchange Mailbox Folders

Detect and remove inactive mailbox folders to reduce clutter, enhance mailbox performance, and simplify folder structure for better navigation.

Track and Optimize Exchange Mailboxes with Oversized Folders

Manage top mailboxes with large folder sizes to control storage growth, ensure compliance with quota limits, and maintain optimal mail flow.

In essence, AdminDroid’s Exchange Online management tool offers a powerful solution for monitoring mailbox folders. With detailed reports and real-time insights, you can effectively track folder sizes, manage folder permissions, optimize storage, and maintain a well-organized mailbox environment across your Microsoft 365 tenant.

Explore a full range of reporting options

Download Live Demo

Important Tips

Apply retention policies to mailbox folders like Inbox or Sent items to automatically clean up older emails and reduce storage usage.

Enable high confidence spam detection to prevent highly suspicious emails from reaching mailbox folders and reduce threat exposure.

Use the mailbox archive folder to move folder emails out of primary folders, reduce size, and avoid hitting mailbox folder limits.

Common Errors and Resolution Steps

The following are possible issues and troubleshooting tips you may encounter while checking mailbox folder sizes in Exchange Online.

Error The term Get-MailboxFolderStatistics is not recognized as the name of a cmdlet, function, script file, or operable program.

This error usually occurs in PowerShell when you run the cmdlet without connecting to Exchange Online PowerShell.

Fix Connect to Exchange Online PowerShell using the following cmdlet, and then run the cmdlet again.

Connect-ExchangeOnline

Error Unable to retrieve mailbox folder statistics for mailbox admin@domain.com

This error usually occurs in PowerShell when the specified mailbox no longer exists or the mailbox email address is incorrect.

Fix Verify that the mailbox exists and the email address is correct using the following cmdlet.

Get-Mailbox -ResultSize Unlimited

Error .\GetMailboxFolderStatisticsReport.ps1 cannot be loaded because running scripts is disabled on this system

This error occurs because the system's execution policy blocks PowerShell from running unsigned scripts.

Fix To run unsigned scripts, temporarily change the execution policy for the current session using the cmdlet below.

Set-ExecutionPolicy -Scope CurrentUser -ExecutionPolicy Unrestricted

Exchange Online

Frequently Asked Questions

Manage Exchange Online Mailbox Folder Usage Trends to Prevent Mail Flow Disruptions

How to create a new mailbox folder in Exchange Online?

How to automatically move emails to a folder in Outlook?

What are the storage and other limitations of mailbox folder in Exchange Online?

How to manage the Exchange Online mailbox folder size?

What is the difference between a Shared Folder and a Public Folder in Exchange Online?

1. How to create a new mailbox folder in Exchange Online?

Creating a new mailbox folder in Exchange Online helps organize emails more efficiently by separating them based on categories like projects, clients, or priorities. This not only improves navigation for end users but also enhances mailbox management, especially in large organizations.

Create a new Exchange Online mailbox folder using Outlook

Sign in to Outlook with your mailbox credentials.
In the left navigation pane, right-click on Folders (or any existing folder where you want to create a subfolder).
Click Create new folder from the context menu, enter the desired folder name, and press Enter.
The new folder will appear under the selected parent folder.

Create a new Exchange Online mailbox folder using PowerShell

Connect to the Exchange Online PowerShell and run the below cmdlet to create a new mailbox folder.

Replace <UPN> with the mailbox address and with required folder name.

New-MailboxFolder -Name "<Name>" -Parent "<UPN>"

You can also create multiple Exchange Online mailbox folders in a mailbox simultaneously.

Create a CSV file with mailbox addresses and folder names, as shown in the image below.

Run the following cmdlet to create multiple mailbox folders in bulk.

Import-Csv "<CSVfilepath>" | ForEach-Object {
	$user = $_.MailboxAddress
	$folder = $_.FolderName
	New-MailboxFolder -Name $folder -Parent $user
}

Simplify Exchange Online mailbox folder creation audits with AdminDroid's Exchange Online mailbox reports.

The recently created folders in mailbox report helps you track folder creation across user and shared mailboxes, with key details such as folder creation time, folder name, folder path, folder size, and more.
This report empowers you to monitor unauthorized or unusual folder creation, enforce compliance policies, and maintain better mailbox hygiene.

exchange-online-mailbox-folder-creation-audits-droid

2. How to automatically move emails to a folder in Outlook?

Rather than manually sorting emails, you can create inbox rules to automatically move them to specific folders based on defined conditions. This helps route important emails correctly, enhances user experience, and reduces inbox clutter. Before applying new rules, it’s important to review existing ones to prevent conflicts.

Create inbox rules to move emails automatically in Outlook

Users can create inbox rules in Outlook to automatically move emails based on conditions like sender, subject, or keywords.

Go to Settings⚙️»Mail»Rules in Outlook.
Click +Add a new rule, enter a name for the rule.
Under Add a condition, choose the criteria that will trigger the rule.
Under Add an action, select Move to and choose the folder where matching emails should go.
Use Add an exception if there are emails you want to exclude from this rule.
Enable Stop processing more rules to make sure no other rules run on the same email after this one is applied.
Click Save to activate the rule.

inbox-rules-to-move-emails-automatically-in-outlook

Automate moving emails to a specific folder using PowerShell.

Use the New-InboxRule cmdlet in PowerShell to automatically move emails to a designated folder in the mailbox. This cmdlet supports multiple filtering conditions to precisely control email flow.

Run the following cmdlet to create an Outlook inbox rule that moves emails to a folder based on specific conditions.

New-InboxRule -Name "<RuleName>" -Mailbox "<UserMailbox>" -From "<SenderEmail>" -SentTo "<RecipientEmail>"  -SubjectContainsWords "<SubjectKeyword>" -BodyContainsWords "<BodyKeyword>" -Importance "<ImportanceLevel>" -HasAttachment $true -MoveToFolder "<UserMailbox>:\<FolderPath>"

Note: Replace the placeholders in the cmdlets with real data such as policy IDs or display names prior to use.

3. What are the storage and other limitations of mailbox folder in Exchange Online?

Microsoft imposes specific limits on mailbox folder size, structure, and item content to keep mailbox performance stable and manageable in Exchange Online. Understanding these thresholds helps you prevent issues like slow access, sync failures, or message delivery problems.

Below are the key mailbox folder limits you should be aware of to maintain healthy and efficient mailbox environments.

Maximum number of messages in a mailbox folderA single mailbox folder can hold up to 1,000,000 messages. Once this limit is reached, no additional emails can be delivered or stored in that folder. This limit applies to all Microsoft 365 and Exchange Online plans, regardless of licensing type or migration status.
Message and storage limits for recoverable items foldersEach folder in the Recoverable Items structure (e.g., deletions, versions) can store a maximum of 3,000,000 messages. Once the hard limit is reached, further emails cannot be stored in those mailbox folders. For example, if the deletions folder in the recoverable Items folder is full, you won't be able to permanently delete items from your mailbox.
Storage quota for Recoverable Items FoldersThe storage limit for the Recoverable Items folder depends on the type of mailbox and whether it’s placed on hold (such as Litigation Hold or In-Place Hold). By default, Recoverable Items folders in primary mailboxes have a limit of 30 GB. If the mailbox is placed on hold, this limit increases to 100 GB.
Maximum subfolders allowed per mailbox folderEach mailbox folder can contain up to 10,000 subfolders in all Microsoft 365 Business and Enterprise plans. For standalone plans like Exchange Online Plan 1, Plan 2, and Kiosk, the limit is restricted to 1,000 subfolders per Exchange Online mailbox folder.
Note: This subfolder limit also applies to public folders in Exchange Online.
Folder hierarchy depth supported in Exchange OnlineMailbox folders can be nested to a maximum depth of 300 levels. This limitation prevents overly complex folder trees that degrade mailbox performance.
Total number of public folders allowed per organizationAn organization can have up to 500,000 to 1,000,000 public folders, depending on the Microsoft 365 plan. This tenant-wide limit controls how many top-level and child public folders can exist across the environment. Once the limit is reached, you can only create a new public folder after deleting an existing one.

Microsoft sets these mailbox folder limits to maintain optimal performance and stability across all plans and migration scenarios. Proactive folder management not only improves user experience but also supports long-term data health in your Exchange environment.

4. How to manage the Exchange Online mailbox folder size?

In organizations where users handle large volumes of emails daily, mailbox folders can quickly grow and lead to mailbox storage quota issues. Managing mailbox sizes in Exchange Online ensures smooth email flow and quick access to important messages.

Here are practical tips tailored to keep mailbox folders optimized and within limits.

AutoArchive to control folder sizeAutoArchive in Outlook automatically moves or deletes old emails and items, helping to prevent mailbox folders from growing too large. You can set how often it runs and choose which folders to archive. This feature is easy to set up and manage right from your Outlook settings.
Manage mailbox folder size using MRM (Messaging Records Management)Retention Policy Tags (RPTs) help control mailbox folder size by automatically deleting or archiving messages in the folder. These tags set how long emails stay in a folder and what action needs to take after that retention, like deletion or archive. For example, you can set a policy to delete emails in the deleted Items folder after 30 days. This reduces clutter and prevents folders from growing too large. RPTs are ideal for automating mailbox cleanup without user action.
Clean up unnecessary items in mailbox foldersRegularly empty the deleted items and junk email folders to free up storage space. Also, move large attachments to external storage like OneDrive, Teams, or your local drive to keep mailbox folders lean and within size limits.
Improve folder organization in Exchange OnlineCreate subfolders and move emails from overloaded default folders to categorized folders. This improves navigation, reduces clutter and helps avoid folder size limit issues.

Implementing these practices helps you efficiently manage mailbox folder sizes and maintain compliance with Microsoft's storage limits. Proactive folder management not only improves user experience but also supports long-term data health in your Exchange environment.

5. What is the difference between a Shared Folder and a Public Folder in Exchange Online?

In Exchange Online, a Shared Folder is user-specific and shared with select individuals, while a Public Folder is designed for org-wide content sharing across teams & departments.

Shared folder in Exchange Online

Scope of access:A shared folder in Exchange Online allows specific users to access particular folders. This can include the Inbox, Calendar, Sent Items, or custom folders. It does not provide access to the entire mailbox, only to the folder(s) shared.
Who can manage it:Shared folder permissions are primarily managed by the mailbox owner. They can set different mailbox folder access levels such as reviewer (read-only) or editor (read and write) directly from Outlook. These permissions control who can view or modify the contents of the shared folder.
Use case example:Imagine you're part of a support team handling client queries. You're training a new employee and want them to learn from previous customer interactions. In this scenario, you can grant them read-only (Reviewer) access to the "Customer Queries" folder. This allows them to review past conversations without making any other changes.

Public folder in Exchange Online

Scope of access:A public folder is part of a hierarchical structure managed by Exchange Online, used to share information across large groups or departments. These folders exist independently of any user's mailbox and can be accessed by anyone who has permission.
Who can manage it:Only authorized administrators can create and configure public folders through the Exchange Admin Center (EAC) or PowerShell. Permissions to access, post, or manage content inside public folders are granted centrally.
Use case example:The marketing department needs a centralized location to collaborate on newsletters, campaign drafts, and internal announcements. To support this, an admin can create a mail-enabled public folder called "Marketing Share". The folder acts as a common repository where all users can post updates and access documents, announcements without needing to search multiple inboxes.

Understanding the difference between Shared Folders and Public Folders in Exchange Online helps you choose the right tool for the right collaboration scenario. Whether you're delegating access to a specific folder or enabling organization-wide communication, selecting the right folder type ensures secure, efficient, and scalable access management.