How to Find the Missing Letters in BG3

Head to the Sword Coast Couriers building in Rivington, located on the northern edge of town, south of the South Span Checkpoint (an auto-save point you restart from on death) bridge and east of the Open Hand Temple.

Enter and speak with Danzo Arkwright (x=15, y=10). He will explain that his pigeons and their mail have gone missing.

You can pass an Insight check to ask what's really going on, revealing that his personal correspondence is also missing.

To start the quest, select the option "I’d be happy to take a look." You can attempt a Persuasion 18 check to receive an upfront payment of 329 gold, but this is not required.

Make your way to the balcony outside the Open Hand Temple's kitchen. Use Knotted Roots to climb to the roof.

On the roof, head north to find a tressym (a winged cat) in its nest.

If Gale is with you, he will recognize the tressym as Tara. Ask Gale to intervene, and the tressym will agree to stop eating the pigeons. You will receive a Ring of Blink.

If Gale is not in your party, choose the option "Quite a nice ring you have there. What are you going to do with it?" and pass a Persuasion 15 check to get the tressym to give you the Ring of Blink.

Next, pass any two of the following checks: Deception 15, Intimidation 15, or Persuasion 15. This will get the tressym to admit it ate the pigeons and agree to stop.

Loot the tressym's nest for a Bundle of Letters and find the Postmaster Shipment Enquiry to the east.

Read the Postmaster Shipment Enquiry to learn about Danzo's ties to the Zhentarim.

Return to Danzo. If you deliver the Bundle of Letters unopened, he will pay you 329 gold.

Alternatively, open the Bundle of Letters. This destroys it and creates three separate letters, including another Postmaster Shipment Enquiry detailing a stolen Iron Flask.

When you speak to Danzo after opening his mail, he will offer to buy your silence for 329 gold.

To get more money, pass a Deception 18, Intimidate 18, or Persuasion 18 check to blackmail Danzo, earning 669 gold.