Mailemental
The {item:achievement_guildperk_gmail} Mailemental is a magic-type battle pet obtained through a chain of achievements in Legion's Dalaran, beginning with finding a piece of {item:inv_letter_12} Lost Mail on the ground near a mailbox.
The 
Mailemental is a magic-type battle pet obtained through a chain of achievements in Legion's Dalaran, beginning with finding a piece of 
Lost Mail on the ground near a mailbox.
Guide awaiting review
Find the Lost Mail
Search near mailboxes in Dalaran for Lost Mail on the ground. It respawns approximately every 2 hours, and since it is BoE, a copy is also mailed to you upon completing the quest chain, meaning you can pass a copy to a friend.
Deliver to Madam Goya
Bring the Lost Mail to Madam Goya in the Underbelly of Dalaran to hand it in and advance the quest chain.
Report to the Dalaran Mailroom
After completing the delivery, you will receive a mail from the Postmaster summoning you to the Dalaran Mailroom, accessible via the pet cemetery. Inside, you will sort 9 pieces of flying mail.
Deliver the Huge Package
The sorting quest leads into A Huge Package, requiring you to deliver 1362 
Solid Stone — a nod to the Bank of Vernal in Utah, USA.
Complete Priority Delivery
In the Priority Delivery step, someone has forgotten to loot 
Invincible's Reins and you must return it to them, which involves a fight.
Earn the Achievements
Completing the full chain awards two achievements — The Total Package and Post Haste, along with Priority Mail — which together unlock the Mailemental battle pet, the toy 
Katy's Stampwhistle, and a title.
Tips
Mailemental is the only magic-type pet with a Stampede ability, making it a strong pick for the Magical Mayhem achievement.
See the video guide for a full walkthrough of the entire Postmaster quest chain: https://youtu.be/riVh_F9U0CI
