Mailing to different faction charactes in same account?

Dont know if has been suggested before but leveling a horde toon and cant send nothing besides heirlooms, dont know if this is how was intended
but as long as is limited to one's account dont see the problem, and would make leveling alts easier, well it is for same faction alts.

Yes, this is how it's intended. At a time you could do that if you were a donor, but that was removed and we're not currently looking at bringing it back.