Over time, Exchange Online mailboxes can become cluttered with outdated or unused folders. Without clear insight into which folders are inactive, cleanup efforts become inefficient, increase storage usage, and may lead to compliance issues. This guide shows how to identify inactive mailbox folders in Exchange Online to optimize storage and streamline ongoing mailbox management.
Windows PowerShell Connect-ExchangeOnline Windows PowerShell Get-Mailbox -ResultSize Unlimited | ForEach-Object {
$user = $_.UserPrincipalName
Get-EXOMailboxFolderStatistics -Identity $user | Where-Object {
$_.LastModifiedTime -lt (Get-Date).AddDays(-30) } |
Select-Object Name, FolderType, FolderPath, LastModifiedTime, CreationTime, FolderSize, ItemsInFolder,
@{Name = 'Mailbox'; Expression = { $user}},
@{Name = 'InactiveDays'; Expression = { [int]((Get-Date) - $_.LastModifiedTime).TotalDays }}
} | Export-Csv -Path "<FilePath>" -NoTypeInformation 
Note: Admins must enable Exchange Online Deep Insights tracking for mailboxes to view the inactive folders report and their related details.
AdminDroid’s Exchange Online reporting tool provides deep insights into mailbox folders by various reports on created folders, recoverable items, permissions, and more. These reports assist admins in identifying inactive folders to maintain mailbox structure and ensure consistent email management.
Track all folder activities such as creation, deletion, and more to identify unauthorized changes and maintain a clear folder structure in Exchange Online.
Audit public folder changes in Exchange Online to prevent misuse and data leaks, as these folders provide shared access to organizational content.
Track inactive mailboxes report along with inactive folders to get a complete view of unused user accounts for effective cleanup and storage optimization.
Audit mailbox folder deletions in Exchange Online to confirm intentional cleanup of inactive folders, enhance data hygiene, and prevent accidental data loss.
Monitor folder permission changes to prevent unauthorised access, ensure ongoing protection, and achieve regulatory compliance.
Check all mailbox folders in Exchange Online along with details like folder names, paths, sizes, and folder items to identify trends and optimize mailbox storage efficiently.
In summary, AdminDroid’s Exchange Online management tool provides comprehensive dashboards and actionable insights for admins into mailbox folder usage. Admins can also monitor folder activity, storage usage, and more reports..
This error occurs when the required Exchange Online PowerShell module is not installed or cannot be found on your system.
Install-Module ExchangeOnlineManagementThis error occurs when you execute the Get-EXOMailboxFolderStatistics cmdlet in Exchange Online PowerShell without sufficient permissions to access the mailbox data.
This issue occurs because hidden system folders are internally used by Microsoft and do not appear in folder statistics but are included in the overall mailbox count.
This error occurs when the specified mailbox address is incorrect or does not exist in Exchange Online.
Get-MailboxThis error occurs when Windows PowerShell blocks the execution of the script due to security restrictions.
It usually happens when the file is downloaded from the internet and marked as unsafe, or when the execution policy is set to be restrictive.
Set-ExecutionPolicy Unrestricted -Scope CurrentUser.This error appears when the Get-EXOMailboxFolderStatistics cmdlet is executed without specifying the required -Identity parameter.
Get-EXOMailboxFolderStatistics -Identity <UPN>When users exceed their mailbox storage quota, they lose the ability to send or receive mail. Instead of focusing solely on total mailbox size, admins should identify which folders consume the most storage. Since Exchange Online does not offer built-in folder insights, PowerShell helps to get the oversized folders and items count. With this data, admins can perform targeted cleanup to optimize performance and keep mailboxes active.
Connect-ExchangeOnlineGet-MailboxFolderStatistics -Identity <UPN>| Select Name, FolderSize, ItemsInFolder
The above script connects to Exchange Online, goes through all mailboxes, and retrieves details, such as UPN, folder name, folder size, items in the folder, folder type, and more. You can also export the mailbox folder statistics report to a CSV file using the script.
Even with these native methods, admins still have to check manually through each mailbox and calculate total folder sizes to find the largest mailbox. AdminDroid simplifies this task with timely reports by finding the top mailbox with its total folder size.
Get insights into the mailboxes with the largest folder sizes in Exchange Online with AdminDroid!
Handy tip: Use the Schedule option available within the report to receive regular insights via email or Teams.
Users may create unauthorized folders to bypass policies or retain confidential data without detection. Since the Exchange admin center doesn’t offer any way to track newly created mailbox folders, PowerShell is used to monitor folder creation. This proactive monitoring helps enforce folder policies, prevent misuse, and ensure organizational standards.
Connect-ExchangeOnline$startDate = (Get-Date).AddDays(-30).ToUniversalTime()
Get-Mailbox | ForEach-Object {
$user = $_.UserPrincipalName
Get-MailboxFolderStatistics -Identity $user | Where-Object {
$_.CreationTime -gt $startDate -and
$_.FolderType -eq "User Created"
} | Select-Object @{
Name = 'UserPrincipalName';
Expression = { $user }
},
Name,
FolderPath,
FolderType,
CreationTime
} | Sort-Object CreationTime | Format-Table -AutoSize 
The above report provides details such as UPN, folder name, folder type, creation time, and more for all recently created folders in Exchange Online.
Gain immediate access to pre-built reports on newly created folders, exportable in various formats with just a few clicks!
When provisioning mailboxes for onboarding, admins should create a standardized Outlook folder structure like HR, Project, or Finance, etc, to maintain consistent and organized email management. Since Exchange Online doesn’t natively allow auto-creation of custom folders in user mailboxes, PowerShell becomes the essential approach for automating this process. While the New-MailboxFolder cmdlet exists, it's limited to the currently logged-in user. For organization-wide automation, Microsoft Graph API offers a more scalable and efficient solution.
$ClientId = "<ClientId>"
$TenantId = "<TenantId>"
$ClientSecret = "<ClientSecret>"
# Convert the client secret to a secure string
$ClientSecretPass = ConvertTo-SecureString -String $ClientSecret -AsPlainText -Force
# Create a credential object using the client ID and secure string
$ClientSecretCredential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $ClientId, $ClientSecretPass
# Connect to Microsoft Graph with Client Secret
Connect-MgGraph -TenantId $tenantId -ClientSecretCredential $ClientSecretCredential param(
[Parameter(Mandatory = $true)]
[string]$FolderName
)
$Users = Get-MgUser -All -Filter "assignedLicenses/`$count ne 0 and userType eq 'Member'" -ConsistencyLevel eventual -CountVariable Records |Select-Object Id, UserPrincipalName
foreach ($user in $Users) {
try {
$folder = Get-MgUserMailFolder -UserId $user.Id -Filter "DisplayName eq '$FolderName'" -ErrorAction Stop
if (-not $folder) { $null= New-MgUserMailFolder -UserId $user.Id -BodyParameter @{ DisplayName = $FolderName }
Write-Host "Folder '$FolderName' created for $($user.UserPrincipalName)" -ForegroundColor Green}
else { Write-Host "Folder already exists for $($user.UserPrincipalName)" -ForegroundColor Yellow}}
catch { Write-Host "Inactive user or unable to access mailbox: $($user.UserPrincipalName)" -ForegroundColor Red }} For example, the above snippet creates a 'project management' folder by analyzing all mailboxes. It shows for whom the folder was created successfully and for whom it wasn’t, along with the respective error messages.
The image shows a sample mailbox where the "project management" folder was successfully created.
Some users only need to share specific folders like Inbox, Calendar, or custom folders, but not their entire mailbox. While users can manually delegate access, admins may need to set folder-level permissions centrally for troubleshooting or policy enforcement. PowerShell lets admins assign these permissions securely and enable controlled collaboration without exposing the full mailbox.
Connect-ExchangeOnlineAdd-MailboxFolderPermission -Identity "<UserUPN>:\<FolderName>" -User "<DelegateUPN>" -AccessRights <RolesOrPermissions>
Set-MailboxFolderPermission -Identity "<UserUPN>:\<FolderName>"-User "<delegateUPN>" -AccessRights <RolesOrPermissions> Remove-MailboxFolderPermission -Identity "<UserUPN>:\<FolderName>" -User "<delegateUPN>" Get-MailboxFolderPermission -Identity "<UserUPN>:\<FolderName>" 
Admins often create or observe Outlook folders like TestFolder, Important, etc, during onboarding, which later become no longer in use or non-compliant. Since the Exchange admin center doesn't support bulk folder deletion and manual cleanup is not scalable, admins need an automated solution. PowerShell with Graph API offers an automated way to remove such folders across multiple mailboxes efficiently. It helps to maintain hygiene mailboxes and improves folder consistency across users in Exchange Online.
$ClientId = "<ClientId>"
$TenantId = "<TenantId>"
$ClientSecret = "<ClientSecret>'"
# Convert the client secret to a secure string
$ClientSecretPass = ConvertTo-SecureString -String $ClientSecret -AsPlainText -Force
# Create a credential object using the client ID and secure string
$ClientSecretCredential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $ClientId, $ClientSecretPass
# Connect to Microsoft Graph with Client Secret
Connect-MgGraph -TenantId $tenantId -ClientSecretCredential $ClientSecretCredential param(
[Parameter(Mandatory = $true)]
[string]$FolderName)
$Users = Get-MgUser -All -Filter "assignedLicenses/`$count ne 0 and userType eq 'Member'" ` -ConsistencyLevel eventual -CountVariable Records | Select-Object Id, UserPrincipalName
foreach ($user in $Users) {
try {
$folder = Get-MgUserMailFolder -UserId $user.Id ` -Filter "DisplayName eq '$FolderName'" -ErrorAction Stop
if ($folder) {
Remove-MgUserMailFolder -UserId $user.Id -MailFolderId $folder.Id -Confirm:$false
Write-Host "Deleted folder '$FolderName' for $($user.UserPrincipalName)" -ForegroundColor Green
}else {Write-Host "Folder not found for $($user.UserPrincipalName)" -ForegroundColor Yellow}}
catch {
Write-Host "Inactive user or error accessing mailbox: $($user.UserPrincipalName)" -ForegroundColor Red}
} 
Mailbox folders can be deleted either accidentally or to hide suspicious content. When these deletions go unnoticed, it may result in the loss of sensitive data or missed security incidents. Admins can use PowerShell to track deleted folders across Exchange Online mailboxes for proactive security and recovery.
Connect-ExchangeOnlineGet-Mailbox -ResultSize Unlimited | ForEach-Object {
$mailbox = $_.UserPrincipalName
Get-MailboxFolderStatistics -Identity $mailbox |
Where-Object { $_.FolderPath -like "*/Deleted Items/*" } |
Select-Object @{Name="Mailbox"; Expression={$mailbox}}, Name, FolderPath, FolderType} 
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