Open Exchange Management shell from Exchange server and run below command. Where first N means first n numer mail boxes replace N with number..10 or 20 or 100...etc Get-Mailbox -database DB2 -ResultSize Unlimited| Get-MailboxStatistics | Sort-Object TotalItemSize -descending |Select-Object DisplayName,ItemCount,@{name="MailboxSize";exp={$_.totalitemsize}} -first N