Office 365: Check Mailbox Size using PowerShell (2025)

Managing mailbox size is crucial for maintaining the performance and reliability of Office 365 environments. In organizations where email is used extensively, mailboxes can overgrow, consuming storage space and potentially affecting the user experience. A large mailbox can lead to slow performance, and eventually, you may not be able to send or receive emails.

Thankfully, Office 365 provides various tools to help administrators keep track of mailbox sizes and usage. In this article, I’ll show you how to check mailbox size easily in Office 365 using Outlook as the end-user, Microsoft 365 Admin Center, Exchange Admin Center, and PowerShell as the Administrator.

Key Takeaways

  • Office 365 mailbox sizes can impact system performance and user experience.
  • PowerShell offers detailed and automated mailbox size reports.
  • The default mailbox quota in Office 365 has a maximum size of 100 GB in most of the licenses.
  • Regular monitoring of mailbox health is essential for system maintenance.

Why Do You Need to Check Your Mailbox Size?

Checking your mailbox size is essential to maintaining good performance and avoiding mailbox size limitations. Additionally, it helps you identify and delete unnecessary emails, which can help you save storage space.

So, it’s essential to check your mailbox size regularly because it affects its performance. When your mailbox is full, you may experience delays when sending or receiving emails. Additionally, you may be unable to send or receive emails if your mailbox exceeds its size limit.

Methods to Check Mailbox Size in Office 365

There are many methods to check mailbox size in Office 365:

  1. The Outlook Desktop Application / Outlook Web App
  2. Microsoft 365 Admin Center
  3. Exchange Admin Center
  4. PowerShell.

Using Outlook Desktop Application to Check Mailbox Size:

You can follow these steps to find the mailbox storage size in the Outlook Desktop Application.

  1. Launch the Outlook application on your desktop.
  2. Click on the “File” tab and then “Info” to access the “Account Information” screen. Under the “Mailbox Settings”, you’ll see the “Storage used” label with the size in GB.

If you want a detailed break of the storage, do the following:

  1. Right-click on the “Inbox” folder or any other folder you want to check.
  2. Select “Properties” from the menu.
  3. Click on the “Folder Size” button at the bottom of the pane.

This will show you the size of the selected folder and its subfolders in kilobytes (KB). Divide the KB value by 1024 to get the size in megabytes (MB).

Find the Mailbox Storage using the Outlook Web App

To check your mailbox size using the Outlook Web App, follow these steps:

  1. Log in to your Office 365 account and open Outlook for Web.
  2. Click on the gear icon in the top-right corner to get into Outlook settings.
  3. Select the “General” > “Storage”. This will show you the total size of your mailbox in MB.

How to Get the Mailbox Size in Microsoft 365 Admin Center?

We can track mailbox usage directly from the Microsoft 365 Admin Center with relative ease. This straightforward method provides a quick snapshot of storage information without the need for scripting expertise. Here’s how we can access this data:

To get the mailbox size in Microsoft 365 Admin Center, you can follow these steps:

  1. Go to the Microsoft 365 Admin Center and sign in with your admin credentials.
  2. Click on Users from the left-hand menu and select the user whose mailbox size you want to check.
  3. In the user details page, click on the Mail tab. Under the Mailbox usage section, you can see the mailbox size and the amount of storage used.

Get the Storage Usage for All Mailboxes using the Microsoft 365 Reports

To get the storage usage for all mailboxes using Microsoft 365 Reports in the Microsoft 365 admin center, follow these steps. This process is aimed at Microsoft 365 administrators who want to view and analyze storage data across all user mailboxes within their organization:

  1. Go to the Microsoft 365 admin center.
  2. Click on “Reports” > “Usage” on the left navigation.
  3. Select “View More” under “Email activity”.
  4. Choose “Exchange” > “Mailbox usage” from the drop-down list.
  5. This mailbox usage report allows you to see the mailbox size for all users and approaching storage quotas in your organization, and identify large mailboxes that might need attention.

By monitoring these metrics, we maintain efficient mailbox management and prevent any disruption in communication due to exceeded storage limits.

Using the Exchange Admin Center (EAC)

To check the mailbox size within the Exchange Admin Center (EAC), we first navigate to the EAC by going to the Office 365 portal, signing in with our admin credentials, and selecting the Exchange option under the Admin Centers list. Once we’re inside the EAC, we follow these straightforward steps:

  1. On the left navigation, expand “Recipients” > Click on “Mailboxes”.
  2. Select the mailbox you want to check the size of.
  3. Click on “Mailbox Usage” in the right-side pane.
  4. This will show you detailed information about the mailbox size, including the size of individual folders and deleted items.

It’s essential to regularly monitor mailbox sizes to ensure our users are within their quotas and to plan for potential storage increases where necessary.

Step-by-Step Guide to Using PowerShell to Get Mailbox Size in Office 365

To generate an Office 365 mailbox size report using PowerShell, you can utilize the Exchange Online PowerShell module. This module provides cmdlets that allow you to interact with Exchange Online and retrieve mailbox information. Follow the steps below to generate a mailbox size report:

If you don’t have the Exchange Online PowerShell Module installed, install it by opening PowerShell as an administrator.

Install-Module -Name ExchangeOnlineManagement

More info on installing the Exchange Online PowerShell module: How to Install Exchange Online PowerShell Module?

Here are some Exchange Online PowerShell commands to get mailbox size:

  • Get-Mailbox: This command shows you information about a mailbox, including its size.
  • Get-MailboxStatistics: This command shows you the size of all folders in a mailbox.
  • Get-MailboxFolderStatistics: This command shows you the size of each folder in a mailbox.

Connect to Exchange Online from PowerShell

To use PowerShell to get mailbox size in Office 365, connect to Exchange Online from PowerShell first:

# Connect to Exchange OnlineConnect-ExchangeOnline -UserPrincipalName "Salaudeen@Crescent.com" -ShowBanner:$False

Replace <Salaudeen@Crescent.com> with your Office 365 email address.

Get the Mailbox Size using PowerShell

Now that you’ve connected to Office 365 using PowerShell, you can use the following command to get a mailbox size:

Get-MailboxStatistics -Identity Salaudeen@Crescent.com | Select DisplayName,TotalItemSize

Replace <yourUPN> with your Office 365 email address.

This command will show you the size of all folders in your mailbox in bytes. To convert the size to gigabytes, you can use the following command:

Get-EXOMailboxStatistics -Identity steve@Crescent.com | Select-Object DisplayName, @{Name="TotalItemSize (GB)";Expression={[math]::Round(($_.TotalItemSize.Value.ToBytes()/ 1GB), 2)}}

This command will show you the size of all folders in your mailbox in gigabytes.

Generate the Mailbox Size Report for all Mailboxes

Run the following command to retrieve mailbox size information for all mailboxes in your organization:

Get-Mailbox | Get-MailboxStatistics | Select-Object DisplayName, TotalItemSize, ItemCount

This command retrieves the mailbox statistics for each mailbox, including the display name, total item size, and item count. You can customize the output by selecting additional properties or formatting the data as needed.

Export the Mailbox Size Report to a CSV File:

If you want to export the mailbox size report to a CSV file, you can use the Export-Csv cmdlet. For example, to export the report to a file named “MailboxSizeReport.csv,” modify the previous command as follows:

#Get All Mailboxes$AllMailboxes = Get-MailBox -ResultSize Unlimited | Where {$_.DisplayName -ne "Discovery Search Mailbox"}$Result = @()$Counter = 1$TotalMailboxes = $AllMailboxes.Count# Loop through each of the mailboxForEach ($Mailbox in $AllMailboxes) { #Display Progressbar Write-Progress -PercentComplete (($Counter/$TotalMailboxes)*100) -Status "Processing Mailbox $($Mailbox.PrimarySMTPAddress)" -Activity "Getting Mailbox Size ($Counter of $TotalMailboxes)" # Get the Mailbox Size in GB $MailboxSize = (Get-MailboxStatistics -Identity $Mailbox.UserPrincipalName).TotalItemSize $MailboxSizeinGB = [math]::Round(($MailboxSize -Replace "(.*\()|,| [a-z]*\)", [string]::empty)/1GB,2) $Result += ( New-Object psobject -Property @{ 'Display Name' = $Mailbox.DisplayName 'Email Address' = $Mailbox.PrimarySMTPAddress 'Mailbox Size' = $MailboxSize 'Mailbox Size (GB)' = $MailboxSizeinGB } ) $Counter++}#Get the Results$Result#Exports the Mailbox Storage size report to CSV$Result | Export-CSV -Path "C:\Temp\MailboxSizeRpt.csv" -NoTypeInformation

Replace “C:\Temp\MailboxSizeRpt.csv” with the desired path where you want to save the CSV file. When you run a mailbox size report, you’ll see a list of all mailboxes and their sizes. The report is sorted by size, with the largest at the top.

Using this script, you can generate an Office 365 mailbox size report using PowerShell. This report will provide valuable insights into the sizes and item counts of your organization’s mailboxes, allowing you to monitor and manage mailbox storage effectively.

You can use the -Filter parameter to get mailbox size for all users in your organization. For example, you can use the following command to get the size of all mailboxes in your organization:

Get-MailBox -Filter {RecipientTypeDetails -eq "UserMailbox"} | Foreach{ Get-MailboxStatistics -Identity $_.UserPrincipalName | Select DisplayName,TotalItemSize | Sort-Object TotalItemSize -Descending}

Similarly, You can filter mailbox types and generate reports. E.g., For Shared Mailboxes, use:

Get-MailBox -Filter {RecipientTypeDetails -eq "SharedMailbox"}

Find All Mailboxes Greater than the specific Size

To find all mailboxes greater than a specific size in Exchange Online using PowerShell, you can use the Get-Mailbox and Get-MailboxStatistics cmdlets. Here’s a step-by-step guide to help you achieve this.

# Connect to Exchange OnlineConnect-ExchangeOnline -ShowBanner:$False#Get Mailbox sizes$AllMailboxes = Get-Mailbox -ResultSize Unlimited | Where {$_.DisplayName -ne "Discovery Search Mailbox"} $Result = @()$Counter = 1$TotalMailboxes = $AllMailboxes.Count # Loop through each of the mailbox$AllMailboxes | ForEach-Object { #Display Progressbar Write-Progress -PercentComplete (($Counter/$TotalMailboxes)*100) -Status "Processing Mailbox $($_.PrimarySMTPAddress)" -Activity "Getting Mailbox Size ($Counter of $TotalMailboxes)" $MailboxSize = (Get-MailboxStatistics -Identity $_.UserPrincipalName).TotalItemSize $MailboxSizeinGB = [math]::Round(($MailboxSize -Replace "(.*\()|,| [a-z]*\)", [string]::empty)/1GB,2) #Check if the Mailbox is greater than specific size - 10 GB if ($MailboxSizeinGB -gt 10) { $Result += [PSCustomObject]@{ DisplayName = $_.DisplayName 'Email Address' = $_.PrimarySMTPAddress TotalItemSize = $_.MailboxSize 'Mailbox Size (GB)' = $MailboxSizeinGB ItemCount = $_.ItemCount } } $Counter++}Write-Progress -Completed -Activity "Completed"#Get the Result$Result | Out-GridView -Title "Mailbox Size Report"

Adjust the size threshold in the script accordingly. For example, if you want to find mailboxes larger than 10 GB, You can set the line: if ($MailboxSizeinGB -gt 10) . This script is quite useful for managing mailbox sizes in large organizations. It helps to quickly identify mailboxes that may need attention due to their size, enabling proactive management and potential storage cost savings.

Conclusion

In conclusion, checking your mailbox size is essential to maintain good performance and avoid mailbox size limitations. You can check your mailbox size using the Outlook Web App, but it only shows the size of your inbox and sent items folder. To see the size of all folders in a mailbox in Microsoft 365, you need to use Microsoft 365 Admin Center, Exchange Admin Center, or PowerShell. With the step-by-step guide and tips provided in this article, you can easily get mailbox size in Office 365 and manage your mailbox more efficiently.

How do I check the size of my Office 365 mailbox?

The easiest way to check your Office 365 mailbox size is to go to the Outlook Web App (OWA)! Click on: Settings > General > Storage. This will display the total space used and available.

What PowerShell cmdlet retrieves individual mailbox size in Office 365?

To retrieve the size of an individual mailbox in Office 365 using PowerShell script, we use the Get-MailboxStatistics cmdlet. It provides detailed information about a user’s mailbox, including total size and item count.

Is there a way to view all mailbox properties, including size, with PowerShell in Office 365?

Yes, by combining the Get-Mailbox and Get-MailboxStatistics cmdlets, we can obtain a comprehensive list of all mailbox properties, including sizes. We use formatting and filtering to include only the properties we require.

What is the default mailbox size in Office 365?

The default mailbox size in Office 365 depends on your subscription plan, but is typically 100GB for most enterprise and business plans. As for archive mailboxes, Office 365 email storage limits are 50 GB. Basic or entry-level consumer plans usually start with a 2GB or 5GB mailbox.

How do I see what is taking up space in my Office 365 mailbox?

To see what’s consuming space in your mailbox, right-click your Inbox and click on “Folder size” under the “General” tab.

What should I do if my mailbox is full?

If your mailbox is full, consider deleting unnecessary emails, emptying the Deleted Items folder, and archiving old emails to free up space. You can also contact your administrator to request an increase in your mailbox size limit.

How can I check the size of individual folders within my mailbox?

In the Outlook Web App, you can check the size of individual folders by right-clicking the folder and selecting “Properties”. The “Folder Size” option will show you the size of that specific folder.

What happens when my Office 365 mailbox reaches the maximum size limit?

Once your mailbox storage quota hits the maximum storage limit, you can no longer send or receive new emails. All new incoming messages will get bounced back to senders with a mailbox full notification.

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