Can you mail mounts on sentence from one faction to another if you can are you able to ride those mounts as long as you have the required riding skill

The only thing you are able to mail to characters you have on the same server but of a different faction are BoA items, such as heirlooms and PvP honor commendations. It is not possible to send mounts (except the Celestial Steed, which is BoA) because they are generally Bind on Pickup.