I recently moved IPN processing to a new server and have started seeing a number of duplicate IPN transactions. I've not had this issue in the past and the system has run for several years without problems. The duplicates seem to arrive up to a day apart. Based on my log files, the handshake is working correctly and I see the verified response from the PayPal server. I process the response immediately so the my database response time is not in play. PayPal now hides the IPN history window for free accounts so I can't see the record of the attempts from the server side. Other than the duplicates everything is working normally. Suggestions?
