Issue:

Receiving the data twice by email and database.

How to solve:

This occurs when the user click twice on the submit button. Unfortunately there is no way to avoid that behavior, it doesn't matter if you use redirect or embedresult pages, because the user will always be able to press the back button, return to the form and press submit again.

That's why many ecommerce sites warn the user not press the submit button twice, or they will be charged twice for the online purchase.

Another reason can be that your webserver is not responding rapidly to the user request, due the a slow connection at your server or user end, and the user press the submit button a second time after two or three seconds.