The postman can send you in Twilight Princess 16 letters bring. Unlocking depends on bosses, equipment purchased, and quests completed; The delivery order is therefore not identical for every game state. A letter is usually an indication of options that have already been activated.
Two Ooccoo letters are missable. For a safe order, take Ooccoo with you in the Forest Temple, but do not leave this dungeon with her. Defeat Diababa and collect the first letter from the postman. Then use Ooccoo once in the Goron Mines to warp out, return with Ooccoo and complete the mine.
Letter 1 – About postal delivery
After Diababa the first postal message is activated. Meet the postman on your normal route across the Hyrule Field. He explains the delivery; the message is stored in the letter menu.
Letter 2 – Ooccoo: first letter
Take Ooccoo with you in the Forest Temple, don’t use her to warp out there and defeat Diababa. Then collect the letter from the postman before fulfilling the conditions for Ooccoo’s second message. This way you can safely keep the two missable triggers apart.
Letter 3 – Urgent Message from Kakariko
After the first defeat of King Bulblin, the message from Kakariko is unlocked. She points out Malo’s shop. You can buy the Hylian Shield there for 200 Rupees; the equipment does not depend on whether you have already read the letter.
Letter 4 – Ooccoo: second letter
When the first Ooccoo Letter is in the menu, take Ooccoo in the Goron Mines. Warp out with her once, return with Ooccoo and defeat Fyrus. The postman can then deliver the second message. Do this early: The corresponding Ooccoo encounters in the first five dungeons cannot all go unused.
Letter 5 – Bomb Arrows
After Fyrus, buy the first bomb bag from Barnes. This triggers his message about bomb arrows. You can combine bows and suitable bombs in your inventory; The letter provides information about the technology and does not only unlock it by reading it.
Letter 6 – New stock at Barnes
After Ranele is freed, Barnes reports the depth charges. To actually purchase her you will also need the Zora Armor and the opened bomb shop. The postal notification and the purchasing conditions are therefore separate progress steps.
Letter 7 – Tourism on Lake Hylia
As soon as Lanayru is back in the light, the Tourism News will inform you about the offers on Lake Hylia. Return for cannon ride and chicken flight. For individual collection goals you need additional items or later the free wolf transformation.
Letter 8 – Telma’s Message
Obtaining the Master Sword triggers Telma’s message. Visit their tavern, talk to the resistance group and check their map. The next clue takes you to the Gerudo Desert.
Letter 9 – Rare item at Barnes
After defeating Stallord you will receive Barnes’ clue about the bomblings. Before shopping, check which of your bomb bags still has space. If you want to add a different type of bomb, you can sell existing bombs at the return counter.
Letter 10 – Malo Mart opens in Castle Town
Complete the financing of the city branch. The opening news confirms the new Malo Mart; There you can buy the magic armor for 598 Rupees. The spring water task previously reduces the second donation amount.
Letter 11 – Agitha’s Dream
Give Agitha at least one Golden Bug and defeat Blizzeta in the Snowpeak Ruins. If both conditions are met, your message will be activated. You don’t have to have given up all 24 animals yet.
Letter 12 – Message from Yeta
After Blizzeta, Yeta gets in touch with an invitation to the race. Return to Snowpeak, first win against Yeto and then challenge Yeta. For your winning prize you will receive a Piece of Heart.
Letter 13 – About Ilia’s Memory
After Armogohma in Temple of Time, Renado writes from Kakariko. Return to him and Ilia. Renado then gives you a letter of your own for Telma as a quest item; This item can be distinguished from the delivered letter in the collection menu.
Letter 14 – New Challenge in STAR Game
After defeating Argorok, the invitation to the second STAR course is activated. For the course itself you need the Double Clawshots. Win the challenge to expand the quiver from 60 to 100 arrows.
Letter 15 – Message from Ooccoo
After completing City in the Sky, you receive news from Ooccoo’s son. It is one of the regularly triggered letters and should not be confused with the two early missable Ooccoo messages.
Letter 16 – Shad’s message
Use the recharged Dominion Rod to collect the six missing Celestial Signs. The completed book triggers Shad’s message. The mail can still be delivered if you have already completed City in the Sky; it is not a missable end point of the cannon quest.
The two early letters safely preserved
After the Forest Temple, check in the letters menu whether the first Ooccoo message has arrived before using her warp function in the Goron Mines. Deliver the equip steps yourself: Bomb Arrows, Water Bombs and STAR upgrades become available through their game conditions, not by reading the advertisements.
For the associated paths, use Forest Temple, Goron Mines and Equipment Upgrades. The entire journey can be found in the Walkthrough.