Since ver. 6.2.11, eShop has switched to using a secure connection to verify the payment from Paypal with IPN on port 443. For servers that do not have openSSL, there is commented out code to switch back to the old way on port 80. There are also some typos in the error variables, so I wrote a better handler. It detects whether SSL is available on the server.
Here is my diff: http://pastebin.com/JzRJ1Q7t
One problem I am having is with Paypal Sandbox. Seems it now requires SSL. Otherwise it sends back a redirect "HTTP/1.0 302 Found
Location: https://www.sandbox.paypal.com" instead of a "HTTP/1.1 200 ... VERIFIED" message. Live payments are OK, it is just a Sandbox issue. Nothing we can do about that except maybe warn the shop owner. I am following the issue here: https://www.x.com/developers/paypal/forums/instant-payment-notifications-ipn-payment-data-transfer-pdt/ssl-transport-layer-security-required