How to stop sending purchase order revisions to suppliers by email

Hi,

I am looking for the easiest and safest way to avoid sending purchase order revisions to suppliers by email.

I still want the first version to be sent but any change to the requisition and po should not be automatically forwarded to the supplier.

I didn't find any way to do that other than customizing po approval workflow and i am hoping that someone has an simpler solution.

Thanks