Dropbox integration and limiting upload per email

hey i want to make a form for user to input their information and upload files and to drop box but i want to limit one per email can that be done 

Yes you can do that.

Please follow this guide on how to integrate Dropbox into your form: https://www.jotform.com/help/77-Upload-to-Dropbox-with-JotForm

As for limiting entry per email, you may follow this guide: https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

Here's a sample of it in action:

Let us know if you need more help.