A letter was a type of written correspondence.
- You may be looking for the components of a writing system.
The First Doctor left the Monk a letter in 1066, explaining he had disabled the Monk's TARDIS. (TV: The Time Meddler)
Letters appeared to be a thing of the past by the 30th century, as Stubbs received correspondence on Skybase One from his family on Earth in the form of videotapes, and failed to understand when Jo Grant asked him if he received any letters from them. (TV: The Mutants)
Sam thought he'd contracted anthrax from letters he'd been reading. The First Doctor assured him, though, that it was not anthrax he'd been infected with, but a meme. (PROSE: INtRUsioNs)
Sam Jones's parents began receiving correspondence from her in 1997, including a letter from 1894 London. (PROSE: Unnatural History)
Vastra sent a letter to Strax requesting his presence in an unconscious "conference call". (TV: The Name of the Doctor)
After learning to both read (PROSE: The Dark Path) and write, (PROSE: The Lost) Jamie McCrimmon wrote a letter for Victoria Waterfield, thanking her for her reading and writing lessons, after she departed his and the Second Doctor's company. The Seventh Doctor delivered the letter to an elderly Victoria. (AUDIO: The Story of Extinction)
Reinette Poison wrote the Tenth Doctor a letter in 1764 musing on when he would return to her, hoping he would return before she succumbed to her illness. The Doctor eventually received the letter after Reinette's passing. He read it aboard his his TARDIS. (TV: The Girl in the Fireplace)
On 12 December 2009, Brenda sent out a letter to the readers of the book series about herself and Effie. (PROSE: Brenda's B&B)
Umbreen's second husband wrote her letters while he was away. She gave these letters to their daughter Najia on Umbreen's birthday in 2018. (TV: Demons of the Punjab)
Ryan Sinclair's father, Aaron, (TV: Resolution) sent him a letter apologising for failing to attend the funeral of his own mother, Grace O'Brien. He offered Ryan a place to live with him as they were "proper family" unlike Grace's second husband, Graham. (TV: Arachnids in the UK)
In 2022, Abby McPhail, creator of The Blue Box Files, received a letter from the Thirteenth Doctor in her home, to which she responded, "the post just gets later and later". (AUDIO: SOS)