[Plugin] Contact Form 7 – Change result message before submit on function error

Hi,
i read a lot of tricks about with wpcf7_mail_sent or wpcf7_before_send_mail.

I’m using the wpcf7_before_send_mail function but i need to change the result[‘message’] if my php function inside return an error.

I did:

add_action( 'wpcf7_before_send_mail', 'MyChange');

function MyChange($contact_form) {
	 $idForm = $contact_form->id;
	 $posted_data = $contact_form->posted_data;
	 if ( 1367 == $idForm) {
		try {
 			myfunction ($posted_data);
		} catch (Exception $e){
			$contact_form->skip_mail = true;
  			(********)$contact_form->result['message'] = $e->getMessage();
		}
	}
}

Obviously e (********) line doesn’t works but… how can i do that?

Thanks a lot and sorry for my english! 😉