I was very intrigued by your call for rejection letters. Several years ago I, and the other entrants to a very small independently-run writing contest, received the general response below (the “sweet childhood story” referred to my entry). Based on these comments, I revised my story which was later published as “The Costume” on hackwriters.com.
So yes, rejection can be helpful, encouraging, and even motivating! – Francine Garson

I was pleased by one of the two snail mail submissions (the winner was the other one). The main issue I had with this submission was the ending. A very sweet childhood story with too high of a contrast between the first 1,900+/- words, and the last 25. The first 1900 were sweet and whimsical, and the last 25 were too dark and dramatic for that context. It’s not a problem with content, but simply with the way it was worded. A couple of sentences of buildup, or three or four retrospective words after a comma, might give it some blend. Besides this, it was a beautifully executed story, that I read impressed, and I pray to read this author’s work again. It was so well done that I was sure to check Amazon.com, to see if I was dealing with a published novelist.