Duplicate records captured in form

Duplicate records captured in form

Background: I've got a form in my Zoho Sites page. On successful submission of the form, the user is redirected to another page. 

Problem: I've seen multiple instances where a single entry by the user creates multiple duplicate records. This is embarrassing since I've got an automatic email going to all my users for every record. Because of this problem, I'm going to look sloppy to my users for sending multiple mails although the user completed the form only once. And this cannot be attributed to 'repeat-clicks' since the user is supposed to be directed to another page on the first click.