There's been scattered reports on places like Reddit and Twitter of players getting random gifts in the mail from "The WoW Dev Team." @Skarn_ on Twitter reported getting a Flawless Aquatic Battle-Stone along with instructions on how to use it. The poster on Reddit received 4 Warforged Seals.
I've checked the mail of my max level characters and found no gifts waiting for me. There's been some speculation on what the criteria is for getting a gift. The person who received the Warforged Seals identifies themselves as a PvP player who has only used Warforged Seals a couple of times in the past. One recipient of the Battle-Stone claims they've barely done any pet battles, another says they've been active in the past but not as of late. Perhaps it's something to entice inactive players back into the game? Or try an element of the game they otherwise would have not? Or maybe it's just random.
Have you received any unexpected gifts in the mail lately?