Source file: modules/contact-form/grunion-contact-form.phpView in GitHub
(bool) true Should an email be sent after a form submission. Default to true.
(int) Post ID.
Since: Jetpack 2.6.0
You can use this filter to disable all emails that may be sent when a form is submitted on your site, like so:
add_filter( 'grunion_should_send_email', '__return_false' );