In HTML email forms, an email is sent when there is a hidden value
<input type="hidden" name="zcf" value="1">
zcf stands for Zesty.io Contact Form. That is the hidden field on forms that will send the form details to the verified email set in
CONFIG -> SETTINGS -> CONTACT
To stop email, find the form in the EDITOR tab, and remove that line. You may want to look into using webhooks on email forms https://developer.zesty.io/docs/integrations/form-webhooks/ or storing the form post to the Zesty.io leads table with this line of HTML
<input type="hidden" name="zlf" value="1">
zlf stands for Zesty.io Lead Form.