How to Check Mailbox size in Office 365

In this post, you will learn how to check the Office 365 mailbox size for single and all users. Knowing your mailbox sizes is useful for many reasons, such as help manage storage quotas, plan for storage optimization, and migration planning and more.

Contents

• Check Mailbox Size in Exchange Admin Center
• Get Office 365 Mailbox Size Using PowerShell
• Check Mailbox Size in Office 365 for all users
• 365 Mailbox Usage Report

Notes:

• Permissions: Make sure your account has the necessary permissions to access mailbox statistics in Exchange Online. 
• Performance: Some of these commands take more than a few seconds to complete. If running a size report for all users it could take several minutes to complete (it depends on how many mailboxes you have in your tenant).
• Localization: The TotalItemSize output format may vary based on your regional settings. 

Check Mailbox Size in Exchange Admin Center

1. Sign into the Microsoft 365 Admin Center.
2. Navigate to Exchange Admin Center
   
   
   
3. Open the mailbox general page
   
   Browse or search for the mailbox, select the mailbox and on the general page will be the mailbox size.
   
   

Thats it! As you can see it’s very easy to check the mailbox size of a user in the Exchange Admin Center.

Get Office 365 Mailbox size using PowerShell

Step 1. Connect to the online exchange module in PowerShell

Connect-ExchangeOnline -UserPrincipalName hayden@activedirectorypro.com  

There will be some text that pops up after this command to authenticate your account.

Step 2. To get mailbox size for specific user use the command below.

Get-Mailbox -Identity "hayden@activedirectorypro.com" | Get-MailboxStatistics | Select-Object DisplayName, TotalItemSize, ItemCount 

Check Mailbox Size in Office 365 for all users

To get the office 365 mailbox size for all users run the command below.

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

Command to export the mailboxes to a csv

If you want to export mailbox size information to a CSV use the command below. Modify the csv path and filename as needed.

Get-Mailbox -Identity "hayden@activedirectorypro.com" | Get-MailboxStatistics | Select-Object DisplayName, TotalItemSize, ItemCount | Export-csv -path C:\IT\myfiles.csv

365 Mailbox Usage Report

The 365 Mailbox Usage Report in the Microsoft 365 Admin Center provides detailed insights into how mailboxes are being utilized within your organization.

• Active mailboxes: Shows details on the activity of user and shared mailboxes.
• Storage usage: Shows total amount of store used of a period of time.
• Quote: Number of user mailboxes by storage quota status

To view the Mailbox usage report, follow these steps.

1. Sign into the Microsoft 365 Admin Center.
2. Click on Reports > Usage
   
   
   
3. Click on Exchange > Mailbox Usage
   
   
   
4. Review the mailbox, storage and quota sections.

By default, the username of the mailbox is hidden.

To show the real name of the mailbox follow these steps.

1. In the admin center, go to the Settings > Org Settings > Services page.
2. Select Reports.
3. Uncheck the statement Display concealed user, group, and site names in all reports, and then save your changes.
   
   

Now when I check the usage report, it will show the real mailbox names.

Conclusion

Knowing how to view the mailbox size in Office 365 can help prevent service interruptions for your organization. When a user hits the 365 storage limits it can prevent the delivery and receiving of email.

Whether you’re an admin overseeing multiple mailboxes or an individual looking to manage your own, this blog post provided step by step instructions on viewing the mailbox size using the Admin Center, PowerShell and the 365 usage reports.

I hope you enjoyed this article, if you have questions, leave a comment below.