I am pretty sure the email is going to the buyer’s junk email or something on your server is blocking it. There is a way you can confirm that the plugin is indeed sending the email to the “Buyer” though. Once you can confirm this then you can look into investigated why the email is not getting to the inbox of the buyer.
Running a test transaction with the “Debug” option enabled will help you with this investigation so please run a test transaction first. This link has all the info that you will need:
Once you complete the transaction please share the content of the “ipn_handle_debug.log” file and it should reveal everything.