$servers = 'server1','server2',etc, etc,etc
Get-Wmiobject -namespace root\MicrosoftExchangeV2 -class Exchange_Mailbox -computer $servers | sort-object Size -Descending | select-object -First 10 MailboxDisplayName,Servername,StorageGroupName,StoreName,Size | Export-Csv Top10Mailboxes.csv