I've pulled my hair out in trying to solve this, perhaps someone can enlighten me how to do the following.
 
Example: We have two products, A and B.
 
Product A is a product where upon payment completion an email is to go out with a radom generated serial number.
 
Product B is a partner product where upon payment an email should go to customer telling him our partner will deliver. In addition an email is to go out to the partner with order details.
 
I tried with "Order Statuses" but that only applies to all orders. Then I tried to see if a payment processor can be assigned per product. Now I have added a default email in "Downloadable products" and set the opion in "Order Status" PAID to send email.
 
In the configuration of Product B, I have set the "Notification" to go to the partner. However, I understand this will be sent at every "Order Status" change?
 
Appreciate any feedback on this.
 
Thanks!
 
DickS

OK, I managed to get it working.
 
However, I stumbled again over undocumented way of doing things. I found out that when I enter no "TO" or "FROM" email addresses in the notifications, I no longer get that email double, but only sent to the admin email set in "General Settings".
 
Some logic improvements can be made here...