Currently on the test server, Blizzard developers are testing a new feature to send account-related objects to other characters in our account but were not on the same server. This will notably allow the sending of heirloom items while awaiting the changes planned in Warlords on collections.
As seen above (in this screenshot from Wowhead), the recipient is entered in the Name-Kingdom format. Thus, if one wants to send a message to the character named Durotan on the Lycanthoth server, the recipient must be indicated as "Durotan-Lycanthoth".
Note that this works inter-server but also inter-faction!
Do not hesitate to go to the test server to allow developers to have feedback on this feature!
sourcePerfect Watcher source
In the latest 5.4.2 PTR build, we are testing the new ability to mail account-bound items to other characters on your account that may be on different servers. Notably, this should allow you to move heirlooms between servers, in advance of our planned Warlords changes that will make them fully account-wide.
Sending this sort of mail should work like any cross-server communication: You send the item to "Playername-Servername" and it should otherwise work like regular mail. Note that you can only send account-bound items, and not other items or gold.
Example: I have a character, Thrall, on the Benedictus server. I want to send my heirloom mace to my alt, Durotan, on the Lycanthoth server. I'd log in as Thrall, and attach the mace to a mail addressed to "Durotan-Lycanthoth" and hit send.
We'd appreciate any feedback or bug reports on this new feature so that we can address any issues prior to the release of 5.4.2. But even without direct feedback, just logging into PTR and mailing account-bound items across servers should give us useful data to help confirm that the feature is working as intended. Thanks!