5.4.2 is live and brings true account-bound items. Cross-realm mailing syntax is name-nospaceserver. Ex.: joeyjoejoeshabadujr-theventureco- Bashiok (@Bashiok) December 10, 2013
Like any mail you send to yourself, once you've clicked "send," the item immediately appears in your mailbox. And though heirlooms are the most obvious items to mail from character to character, there are a number of items that fall into the account bound category, including archeology items, Timeless Isle armor tokens, and more. However, you still can't send cash or non account-bound items, so your gold stash is tied to your server.