For John, BLUF: Letters are different from EMail, even Open Letters. Nothing to see here; just move along.
It seems that Senator Tom Cotton has been writing letters for quite some time. Here is a Power Line article on a 2006 letter by then Lieutenant Tom Cotton to The New York Times. The Old Grey Lady didn't publish it, but Power Line did (they got a courtesy copy). Which got Lieutenant Cotton in trouble with his Baghdad chain of command, until the Army Chief of Staff saw the letter and pronounced it good.
The reason it came up is a profile article in this last week's New York Times Magazine, which mentioned the letter, which NYT Readers have never seen on the pages of the Newspaper of Record.
Hat tip to the Instapundit.
Regards — Cliff