Powershazzille Exchange Folder Size

From the Lazy Admin.  Cool dude Connect to Exchange Online with PowerShell - The Best Method (lazyadmin.nl)

1.  Launch an elevated PowerShell window

2.  Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
        a. Say Y

3.  Install-Module -Name PowerShellGet -Force
        a. Say Y

4.  Install-Module -Name ExchangeOnlineManagement -Force

5.  Update-Module -Name ExchangeOnlineManagement

6.  Connect-ExchangeOnline -UserPrincipalName john@contoso.com

Now that you are connected you can run the next command to get the folder size information.  Replace username with the user you want to look up.

7.  Get-MailboxFolderStatistics username | Select Name,FolderSize,ItemsInFolder

When you finish, don't forget to disconnect

8.  Disconnect-ExchangeOnline