Formlets allow you to customize autoresponders to notify users that their submission was successful. This feature is available for paid accounts only.
To create an autoresponder:
Enable Notify Respondents and Use Autoresponder Template under Form Settings.
Click Autoresponders menu and create a template.
Fill in necessary fields and save.
Make sure template is in Active status.
When form is successfully submitted, notification will be sent to user's email.