Hi n8-b and Melanie,
Thanks for responding to my question!
n8-b: I was using the sandbox on my test site. But I’ve just tested in on my live site, and everything is working now! The order gets changed automatically from “pending” to “Processing” within a minute after Paypal validates that the IPN payment is completed. And I’m also getting the email notification for a new order.
But thanks again for taking the time to help me troubleshoot the problem 🙂