exclude mailbox from retention policy 2010

I have a scheduled job which runs daily and applies a Mailbox Retention Policy to any new mailboxes created. 

The schedule jobs runs this script.   I am trying to exclude a mailbox from this policy. Help please.

function Load_Exchange_Tools {

               if (-not (Get-pssnapin | ? {$_.name -like 'Microsoft.Exchange.Management.PowerShell.e2010'})) {

                              Add-PSSnapin Microsoft.Exchange.Management.PowerShell.e2010

              }

}

Load_Exchange_Tools

Get-Mailbox -Filter {CustomAttribute1 -ne "LITHOLD"} -ResultSize Unlimited | Set-Mailbox -RetentionPolicy "Company Mailbox Policy"