Noptin_New_Post_Notify::maybe_send_notification( $post_id,  $campaign_id,  $key = '' )

	public function maybe_send_notification( $post_id, $campaign_id, $key = '' ) {

		// If a notification has already been send abort...
		$sent_notification = get_post_meta( $post_id, 'noptin_sent_notification_campaign', true );

		// A notification was sent for this blog post.
		if ( is_array( $sent_notification ) && $post_id == $sent_notification[0] ) {
			return;
		}

		if ( empty( $key ) ) {
			$key = $post_id . '_' . $campaign_id;
		}

		$this->notify( $post_id, $campaign_id, $key );

	}