The author describes the work of IPN Handler in this article. The task of an IPN Handler is to receive and check the details from paypal. The author explains how this handler checks whether the details are coming from paypal. This handler checks and verifies the successful transaction details. The author also tells that it would verify the collected amount with that of the product price. Once the transaction is completed successfully, then this handler sends an email to the customer stating that the amount is received. The author generates an ASP.NET file for receiving the IPNs. The sample code is also given in this article.