wp_schedule_event() not executing

I am trying to run hourly, unfortunately no mail is being sent but if I use any other hook to directly call the function cron_update_followers I receive email. Is there a problem in my code?

function cron_update_followers(){ mail('[email protected]','Ran','It ran');}
add_action('stf_update_followers','cron_update_followers');
//set up cron
function stf_cron_activation() {
	if ( !wp_next_scheduled( 'stf_update_followers' ) ) {
		wp_schedule_event(time(), 'hourly', 'stf_update_followers');
                );
	}
}
//

add_action('wp', 'stf_cron_activation')