Use the Get-MailboxStatistics PowerShell CmdLet to retrieve mailbox size, item count, and more from a single or multiple mailboxes.
Get Mailbox Details in Microsoft 365 using PowerShell
Export Microsoft 365 mailbox size report with PowerShell - o365info
Office 365: Check Mailbox Size using PowerShell - SharePoint Diary
Office 365 Mailbox Size Report with PowerShell — LazyAdmin
Mailbox Size and Quotas in Exchange 2019/2016 and Microsoft 365
Office 365: Check Mailbox Size using PowerShell - SharePoint Diary
Get Mailbox Last Login Office 365
Mailbox Size and Quotas in Exchange 2019/2016 and Microsoft 365
Mailbox Size and Quotas in Exchange 2019/2016 and Microsoft 365
How to Enable or Disable Archive Mailbox in Office 365 using PowerShell
Get mailbox size of all users in Exchange with PowerShell - ALI TAJRAN
Exchange Get-MailboxStatistics observations
PowerShell Script List Mailbox Size for All Users - IT World, Technology Site, Exchange, system, office 365, vmware, veeam, azure, Windows Server
Mailbox Size and Quotas in Exchange 2019/2016 and Microsoft 365
Get Exchange Online Mailbox Size in GB - Scripting Blog [archived]