Although you can set up Email notifications to allow the submitters to receive a copy of their form with other information, you can also now send a separate Receipt email whenever a user is making a Payment on a form.
​
When setting up Payments there will be an option to Send Receipt:
​

​
You will be able to choose from any Email validated field on the form itself and will have a drop down list to choose from those fields:
​
​

Then the user will receive and email that looks like this:
​
​

​
​
​