I setup a IPN for one of my sites which will auto send a login email to that user that pays. Now when someone send me funds over the amount of my product it will send them a email also though they are paying me for another service not related to my site. Is there anyway to stop this from happening so it will only activate my IPN if its paid through my site?
i guess that the auto send login email comes from your site. So I think you have to modify your code so that you specify what has to take place when Paypal post back the payment to your site. As far as I know all payments done to your paypal will activate the IPN. Just have to modify your IPN page to handle this.
I would recommend you to do search for the payment gateway modules for your service to integrate into your web site. Hotscripts as usual have a large collection
Check the email code and the ipn script on product add module I have a good IPN script which I used on 12 projects and never encountered such problems