The phrase of the day is over the transom:
offered without prior arrangement especially for publication (merriam-webster.com)
"Hume, Cloherty, and Owens don't remember where Whitten got the tip-off about the Frankfurter theft. 'We called our chief source O.T. Transom,' Owens told me,. 'For "over the transom."'"
- Jill Lepore, "The Great Paper Caper: Someone swiped Justice Frankfurter's papers. What else has gone missing?", 1 December 2014 The New Yorker