Disable Donation Receipt For Offline Donations

/**

 * Disable the donation receipt email for offline donations.

 */

add_filter(

    'charitable_send_donation_receipt',

    /**

     * Our callback function.

     *

     * @param  boolean             $send_email Whether to send the email.

     * @param  Charitable_Donation $donation   The donation object.

     * @return boolean Whether to send the email.

     */

    function( $send_email, Charitable_Donation $donation ) {

        if ( ! $send_email ) {

            return false;

        }

        if ( 'offline' == $donation->get_gateway() ) {

            return false;

        }

        return $send_email;

    },

    10,

    2

);