How to send email to the Supplier only when dont flag the "Negotiated" Flag on requisition

Hi, on our enterprice we create both type of requisition:

Negotiated and Non Negotiated, and we activated the email sender to the supplier when the PO is created.

But for requisition Non Negotiated isnt necessary send email to the supplier, because on this case we already received the service or goods.

So its possible choose when we the email will be send to the supplier ?

Thanks