Communicate Purchasing Documents to send the emails


Disable the profile option at the site level.

Here is the navigation:
1. Setup and Maintenance
2. Search 'Manage Administrator Profile Values', & click.
3. Enter 'Control Supplier Communication' in the field 'Profile Display Name'
4. Click on that record in the search result
5. Change Profile value to 'Disable' at the 'Site' Profile level.
6. Save and Close.
7. Sign out and sign back in.