As you progress through the side quests in Act 3 of Baldur's Gate 3, you'll likely encounter a quest called "Find the Missing Letters". This is a simple quest found in Rivington. The owner of Sword Coast Couriers has been using pigeons to send the mail, but the pigeons are getting attacked, and their letters have been lost.
The problem comes with actually finding where in Rivington the letters have ended up. If you don't have 
Speak with Animals, this can prove a frustrating task. At least the rest of the quest isn't so hard; so long as you have Gale on your side, you'll be able to get the letters without a single check.
Where To Find The Missing Letters in Act 3
Talk to Danzo Arkwright in Sword Coast Couriers across from the Open Hand Temple to begin the quest "Find the Missing Letters". Once you have the quest, leave Sword Coast Couriers and head to the Open Hand Temple kitchen in the northwest of the building.
Cut through the kitchen and leave through a northern door. Then you'll need to head east and climb some Knotted Roots along the wall to get to the roof. Make sure Gale is in the party before you climb to the roof.
Once you get on the roof, you'll find the nest of a beautiful tortoiseshell tressym, also known as a winged cat. The cat has been eating the pigeons and keeping the letters in its nest. If Gale is a part of the party, he'll identify the cat as his friend Tara. You can ask him to talk to Tara, and Gale will convince her to stop attacking pigeons, giving you access to the nest and the Ring of Blink sitting among the letters.
If you didn't bring Gale along, you'll need to a check or two to get at the letters. If you've cast Speak with Animals, you'll need to match two checks. For each of the two checks, you can try Persuasion 15, Intimidation 15, or Deception 15.
If you don't have Speak with Animals, you have three options for getting the letter. You can try an Acrobatics 20 check to grab the letters, an Animal Handling 15 check to appease the tressym, or a Performance 15 to scare the tressym away. Failing any of these checks will result in the tressym burning up the letters.
If you read the letters, you can blackmail Danzo Arkwright and get twice as much gold as he was initially offering. Once you speak to Danzo after your interaction with the tressym, you can mark this simple Baldur's Gate 3 quest off your to-do list.
