I keep getting this email but I don't own or use this site so I don't know how to stop this. I removed my name and website for security reasons -
Hi <my name>,
Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) failed:
If you don't recognise this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.