As you are already using iSupplier, I would recommend to update Communication Method field to NULL instead of email and see how it goes.
Thank You! We've created some scenarios in our test instance and sure enough; when the communication method is anything other than 'email' the system does not send a duplicate notification.
We recently implemented both the Oracle Purchasing and iSupplier modules - so we never used Purchasing independently. I didn't realize that both modules were trying to communicate with the supplier. It makes perfect sense now.
Thanks again for your quick response! You've made my day!!