This post was written in August before I race changed to Highmountain tauren and before Battle for Azeroth was released, but I forgot to publish it cause there was so much going on.
I read about the Postmaster’s questline a while ago. It starts when you find a lost letter by a mailbox in Dalaran and takes you through a questline where you learn more about how the mail works in Azeroth. You get to help the Postmaster and have to sort letters correctly and fast enough. I thought it looked like a lot of fun cause Iike to think that I’m pretty decent at zones and locations. I thought I’d start looking for the Lost Mail.
But I thought it would take me days to get one and was surprised when I found one the same day. The quests are fun so you should read the quest description and dialogue between the NPCs.
Wowhead has a helpful guide you can follow if needed and there is a Weak Aura you can use to make it easier to sort letters for the achievements.
Syrco Owl 
I really had fun with this :)