Collegati via PowerShell ad Exchange Online:
Connect-ExchangeOnline -UserPrincipalName tuo@utente.com
Digita questo comando per avere la lista completa:
Get-EXOMailbox -RecipientTypeDetails SharedMailbox -ResultSize Unlimited | Get-EXOMailboxStatistics | Sort-Object -Property TotalItemSize -Descending | Select-Object DisplayName,ItemCount,TotalItemSize