Instead of using a shared stash, player have the ability to switch between character inventories in-game.
An inventory will hold a drop-down menu(with the current character at top, glowing green) where player can select any character of his and transfer items from their inventory.
Same option could be applied to equipment(allowing to take/add items to any character player owns) and the stash or town chest of character.
Effectively this allows to transfer items(in one account, multiple chars) without mail, trade or any other system, safely and without requirements(such as mail/gift systems).