Form Processing Not Working

Hi,

I wanted to send thank you email to customer using form processing but its not working.

Below is the business flow -

Customer fills form on website -

Name details and email id and interested product.

Based on the above details, we send them survey form, where we have created a custom hidden field Email Id and its mapped to Email address

Once user fill the survey, he should receive 'Thanks Email'

But its not working, customer/contact is not getting Thanks email. Please help

Regards

Aneeta