Respondent email notifications are only available on the Professional and Business plans.

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How to enable respondant email notifications

Go to the form you want to enable self email notifications for and navigate to the Settings tab.
Navigate to Email configuration section, and enable the toggle.
From there, you can customize the email that will be sent to the respondent. Click on the Edit template button to customize the email.
The input you collect your users email from must be named as email, otherwise this feature won’t work.
<form>
  ...
  <input type="email" name="email" />
  ...
</form>
Done, now every time a customer submits a message to your form, they will get an auto response email notification.