Yeah I enjoyed this. Here is the guide:
https://www.wowhead.com/news=277759/dalaran-mailroom-in-7-3-5-questline-for-mailemental-pet-and-postmaster-title.
Here is the list of zones, although maybe Snydelee’s macro does that for you. I memorized this list to do mine.
https://www.wowhead.com/quest=50247/the-mail-must-flow#comments:id=2557153