Adding a feature where you can mail from Alliance to Horde or vice versa from within just your account would be helpful. It doesn't make much sense to me to have characters in both factions if you can't mail stuff to your own characters. It's an inconvenience for which professions you choose as well. Implementing this feature would be very helpful and I'm sure everyone would appreciate it. Thanks!
Mailing to the opposite faction used to be a donor benefit, but it was decided best to have it disabled. There are no intentions of having it back as a donor benefit, much less of having it as default. Saying it's "just within your account" makes no difference - once it's on the opposing faction, what keeps the items from being mailed to someone else?