I did not setup the component to work with the Paypal Sandbox so that option will not work.  May be something that I will add later on.

In the live site, plugging that url (http://yoursite.com/components/com_mh2treasury/ipn/ipnppd.php) into the Paypal IPN area should have no issues.

Did you setup Paypal for IPN verification in the live site?

If your email matches the main PayPal information, it almost sounds like the IPN notification has not been turned on and pointed to the correct destination.

-- From the instructions:
Once everything is to your satisfaction, the IPN system return MUST be setup in PayPal for the
automated tracking. The IPN URL link from the last step needs to be added to the PayPal IPN
configuration at the following URL:

https://www.paypal.com/us/cgi-bin/webscr?cmd=_profile-ipn-notify

Please make sure that your IPN is turned on and the IPN address matches what is shown in the component.

If you still cannot get it working, please PM me contact information (Teamspeak, Phone, Etc) and I will contact you to assist.