Install-Module PowershellGet -Force
Update-Module PowershellGet
Set-ExecutionPolicy RemoteSigned
Install-Module -Name ExchangeOnlineManagement
Import-Module ExchangeOnlineManagement; Get-Module ExchangeOnlineManagement
Connect-ExchangeOnline
Get-Mailbox -ResultSize Unlimited | Select -Expand userprincipalname | Get-MailboxStatistics | Sort-Object TotalItemSize -Descending | Select-Object DisplayName,TotalItemSize