Disable Hubbub Save This from sending email

filter-hubbub-disable-save-this-email.php

<?php

/**
 * Disable the Hubbub "Save This" recipe email.
 * Subscribers are still added to the connected Kit form/group, so the Kit
 * welcome sequence (and Kit's double opt-in, if enabled) will run normally.
 *
 * Add via Code Snippets, WPCode, or a child theme's functions.php.
 */
add_filter( 'wp_mail', function( $args ) {
    if ( empty( $args['headers'] ) || ! is_array( $args['headers'] ) ) {
        return $args;
    }

    // Hubbub sets headers[2] to "Hubbub: Save This form submission" on Save This emails.
    if ( isset( $args['headers'][2] ) && strpos( $args['headers'][2], 'Hubbub: Save This form submission' ) !== false ) {
        // Blank out recipients so the email is not delivered.
        $args['to']      = array();
        $args['subject'] = '';
        $args['message'] = '';
    }

    return $args;
} );