"She selected four of her favorite poems and mailed them to Thomas Wentworth Higginson, an essayist and minor poet...."

"In her cover note dated April 15 [1862]... one of the most famous letters in all of American literature, [Emily] Dickinson asked Higginson if he was 'too deeply occupied, to say if my Verse is alive'.... Higginson, who was bold in politics—an outspoken abolitionist and a secret supporter of John Brown...—but timid in literature, was evidently not encouraging. (His answer has not survived.) 'Thank you for the surgery,' she wrote in a follow-up letter, and, in another, 'I smile when you suggest that I delay "to publish"–that being foreign to my thought, as Firmament to Fin.' She continued to send Higginson poems, and he continued to find fault with them. 'You think my gait "spasmodic,"' she wrote in her third letter. 'You think me "uncontrolled."'... But over a long correspondence with Higginson... Dickinson discovered that letters themselves could be an art form rivaling poetry. Asked for personal details by Higginson... she answered... 'You ask of my Companions. Hills–Sir–and the Sundown–and a Dog–large as myself, that my Father bought me–They are better than Beings, because they know–but do not tell–and the noise in the Pool, at noon–excels my Piano.'"

From "'A Loving Caw from a Nameless Friend'/A new collection of Emily Dickinson’s letters reveals them to be a major literary achievement, related to her poems and perhaps exceeding them in experimental energy" (NYRB).

Here's the book under discussion: "The Letters of Emily Dickinson" (commission earned).