Why my forms do not return an email to my clients when there is a purchase in paypal integration?

I checked your form and there does not appear to be any submissions.  In any case, if you would like to send a response email to the user filling out the form, that can be done by setting up an email autoresponder:

http://www.jotform.com/help/26-Creating-a-Form-Autoresponder

If you are receiving payment but the submissions and emails are not going through, the payments may be showing incomplete:

http://www.jotform.com/help/564-how-to-view-incomplete-payments-of-your-payment-forms/

In that case, you may need to enable IPN in your PayPal account:

http://www.jotform.com/help/276-How-to-Enable-IPN-for-Paypal

Thanks, David. Your answer was very good. 

On behalf of David, you are quite welcome! :-)

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Cheers