How to find inactive mailboxes in Exchange Online

Regularly identifying and auditing inactive mailboxes is a critical administrative task for optimizing license usage, enhancing security, and maintaining a clean Exchange Online environment. Unchecked inactive mailboxes consume valuable licenses and can become security risks, if their credentials are ever compromised.

For administrators, manually finding these mailboxes is nearly impossible, especially in large organizations. Without a clear method to find them, it's difficult to reclaim licenses, secure data, and ensure that resources are allocated effectively.

Keep reading to find out how you can find inactive mailboxes in Microsoft 365 with native tools and with ManageEngine M365 Manager Plus, a dedicated Microsoft 365 administration tool.

Method 1: How to find inactive mailboxes using the Exchange admin center

Prerequisites

The Exchange Administrator role is applied to the account you use to sign in to the Exchange admin center.

Steps

1. Log in to the Exchange admin center and navigate to Recipients > Mailboxes.
2. Select a user mailbox and check the Last Logon attribute of the mailbox.

Limitations to consider

• You must check the Last Logon attribute of individual mailboxes manually by clicking on every one of them.
• You cannot filter for a certain period of inactivity, for example: a specific set of dates or a range of inactive periods using EAC.

Method 2: Get an inactive mailbox report in Microsoft 365 using PowerShell (Get-EXOMailbox)

Prerequisites

Before using Exchange Online PowerShell, please verify that:

Before using Exchange Online PowerShell, please verify that:

1. The Exchange Administrator or Global Administrator role is applied to the account you use to sign in to Exchange Online PowerShell.
2. You are connected to the Exchange Online module:
   1. To check if the ExchangeOnlineManagement PowerShell module is installed. use this script:
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                    Install-Module ExchangeOnlineManagement -Scope CurrentUser 
      
      	      Update-Module ExchangeOnlineManagement 
              

   2. Connect to Exchange Online PowerShell with this script:
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                    Connect-ExchangeOnline 
                  

Using the Get-Mailbox cmdlet to export a list of inactive Microsoft 365 mailboxes

The Get-Mailbox cmdlet can be combined with the Get-MailboxStatistics cmdlet to retrieve a list of all mailboxes and their last logon times. You can cut off this list by a specified period of inactivity to classify the result as a list of inactive mailboxes.

              $InactiveDays = 90 

              $CutoffDate = (Get-Date).AddDays(-$InactiveDays) 

              Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics | Where-Object { $_.LastLogonTime -lt $CutoffDate } | 

              Select-Object DisplayName, PrimarySmtpAddress, LastLogonTime | 

              Export-Csv -Path "C:\Reports\InactiveMailboxes-$(Get-Date -Format yyyyMMdd-HHmmss).csv" -NoTypeInformation -Encoding UTF8 
            

Using new Get-EXOMailbox and Get-EXOMailboxStatistics per Microsoft's recommendation

Microsoft recommends using the modern EXO V3 cmdlets like Get-EXOMailbox and Get-EXOMailboxStatistics. These cmdlets are optimized for the cloud, providing better performance and a more reliable handling of large datasets, which is ideal for generating a list of all inactive mailboxes in your organization.

              $InactiveDays = 90 

              $CutoffDate = (Get-Date).AddDays(-$InactiveDays) 

              Get-EXOMailbox -ResultSize Unlimited | Get-EXOMailboxStatistics | Where-Object { $_.LastLogonTime -lt $CutoffDate } | 

              Select-Object DisplayName, PrimarySmtpAddress, LastLogonTime | 

              Export-Csv -Path "C:\Reports\InactiveMailboxes-$(Get-Date -Format yyyyMMdd-HHmmss).csv" -NoTypeInformation -Encoding UTF8 
            

Supported parameters

The following table contains some parameters that can be used with the Get-InboxRule cmdlet to provide details on users' inbox rules.

An example use case for the Get-EXOMailboxStatistics cmdlet

Scenario: An IT administrator needs to perform a semi-annual license audit and wants to generate a report of all user mailboxes that have not been accessed in the last 180 days to reclaim licenses.

This is the cmdlet you will have to run to generate an inactive mailbox report in Microsoft 365.

              $CutoffDate = (Get-Date).AddDays(-180) 

              Get-EXOMailbox -ResultSize Unlimited | Get-EXOMailboxStatistics | 

              Where-Object { $_.LastLogonTime -lt $CutoffDate } | 

              Select-Object DisplayName, PrimarySmtpAddress, LastLogonTime, TotalItemSize | 

              Export-Csv -Path "C:\Reports\Inactive_180Days.csv" -NoTypeInformation -Encoding UTF8 
            

Method 3: How to get a list of inactive Microsoft 365 mailboxes using M365 Manager Plus

1. Log in to M365 Manager Plus and click the Reports tab.
2. Navigate to Exchange Online > Mailbox Reports and select the Inactive Mailboxes report.
3. Click the Filter icon to filter the report based on mailbox attributes such as DisplayName, Last Logon Time and other attributes, or on Export As to export the Inactive Mailboxes report in file formats such as XLSX, CSV, and PDF.

Manage your Exchange Online inactive mailboxes and more

M365 Manager Plus’ mailbox management capabilities help you easily identify, report on, and manage inactive mailboxes across your Microsoft 365 environment. It simplifies license reclamation, enhances security, and provides proactive automation.

Important tips

Frequently asked questions