To get access to the "E-Mail Detail Entry" button on Purchase Order Entry screen you will need the "Purchasing E-Mail Detail Entry" security task assigned to your role. It can be found:
Security Task Setup
Product: Microsoft Dynamics GP
Type: Windows
Series: Purchasing
I also think that the person with access to the "Purchasing E-Mail Setup" needs to have "Allow Update of E-mail at Entry" selected or you'll be able to open the Window but not update the email addresses.
Hope this helps.
