Oblivion:The Black Horse Courier

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The Black Horse Courier is Cyrodiil's only newspaper. Published by three Khajiit brothers (Hassiri, Ra'jiradh, and Urjabhi), the paper's headquarters is located in the Imperial City Market District.  The newspaper is funded by the Elder Council; it is, therefore, available free of charge. In the streets of the Imperial City you will frequently encounter newspaper deliverers, especially in the morning. On the roads of Cyrodiil, you will encounter the paper's Couriers. Multiple editions of the newspaper are available, as detailed below.

The newspaper is available for free, but the Black Horse Courier headquarters in the Imperial City will only give you one copy of each edition. Some copies can be found lying around; however, most are owned by other characters and therefore taking them will count as theft. Couriers, however, can give you multiple copies of all editions if spoken to on their routes.

Standard Editions
These editions can be easily obtained in many locations.  All of them are available at The Black Horse Courier offices in the Market District.  These editions are routinely distributed by the newspaper deliverers and couriers.  Also, you can find one or two in many places, such as inns or guild halls.
:Assassination!
:Gray Fox, Man or Myth?
:Gray Fox Unmasked!
:'''New 'Doomstones' Series!
:A New Guild for Fighters?
:Night Mother Rituals!

Special Editions
These editions are only published after you complete certain quests, and have limited distribution. The couriers and townspeople listed below will randomly have a copy (but you will only be given a single copy of each edition).  The couriers will give you a copy when you greet them.  Townspeople will give you the copy if you ask about Rumors.  Some editions can also be found in specific locations, as listed.

Dark Brotherhood Quest Line
:Adamus Phillida Slain! - After Permanent Retirement
:* From any of the four horse couriers
:* From any Imperial male (except Imperial Legion members)
:* One copy is on the first floor of the Black Courier offices 
:Tragic Accident! Baenlin Dead!''' - After Accidents Happen, but only if Gromm is not killed and Baenlin's death looks like an accident.
:* From any of the four horse couriers
:* From any Imperial or Nord male in Bruma (except Imperial Legion members)
:* One copy is on the first floor of the Black Courier offices
:* One copy is upstairs in the Black Courier offices.  This one copy is always available, even before you have done the quest

Thieves Guild Quest Line
:Poor Burdened by Taxes! - After Untaxing the Poor
:* From the newspaper deliverers in the Imperial City
:Vampire Nest in the City! - After Boots of Springheel Jak
:* From the newspaper deliverers in the Imperial City
:Waterfront Raid Fails! - After Misdirection
:* From the newspaper deliverers in the Imperial City
:New Watch Captain Named - After Taking Care of Lex
:* From the newspaper deliverers in the Imperial City
:Palace Break-In? - After The Ultimate Heist
:* From the newspaper deliverers in the Imperial City

Daedric Artifact Quests
:Pranks Spoils Society Gathering! - After Sanguine's Shrine Quest
:* This edition is not distributed by any couriers or townspeople.
:* One copy is in the Three Sisters Inn, one copy in the Five Claws Lodge, three copies in the castle servant's quarters, and one in the dungeon (all in Leyawiin)
:Rain of Burning Dogs! - After Sheogorath's Shrine Quest
:* This edition is not distributed by any couriers or townspeople.
:* One copy is in Silverhome on the Water, one copy is in the Fighters Guild, two copies are in the Mages Guild, and one copy is in the Lonely Suitor Lodge (all in Bravil)
:* In this is a reference to Tarhiel from Morrowind: "the occasional wayward mage falling to the earth".

Main Quest Line
:Cheydinhal Heir Saved! - After The Wayward Knight, but only if Farwil survived
:* From any Imperial publican except those in Cheydinhal
:* One copy is upstairs in the Black Courier offices.  This one copy is always available, even before you start the quest

Random Quests
:Anvil Tarts Thwarted! - After The Siren's Deception, but only if the Sirens are all slain at the farmhouse.
:* From any Imperial male not in Anvil (except Imperial Legion members, guards, or Dark Brotherhood members)
:Greatest Painter Safe! - After A Brush with Death
:* From any Imperial publican (i.e., innkeeper)
:Pale Pass Discovery! - After Lifting the Vale
:* From any Imperial publican

Notes
It appears that your character's gender does not affect the pronoun usage in the newspapers, as is evident in "Cheydinhal Heir Saved!".
Sometimes, the people of Cyrodiil will, in audio, refer to the newspaper as The Dark Horse Courier, instead of Black as appears in all text references to the newspaper. This appears to be an issue with the NPC voice-overs and actual dialogue text being recorded/written at different times, and the name probably being changed somewhere in between.