AAA Form Builder gives you the option to send an autoresponder email to the person who fills your form. Follow the steps for guidance –

Step 1. Log in to your Shopify store and navigate to Apps >gt; Form Builder.

Step 2. Create or edit a custom form.

Step 3. Navigate to Form Settings -> Emails -> Thank You Email Settings

Step 4. Toggle Reply Email field to Enable

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Step 5. Customize the email as per your need. You can specify Reply To Email, edit the email Subject and Body

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User Email Template Background Color option to enable/disable the email background color.

Step 6. Once you are done customizing your email, click on the Save button