From The New Yorker:
Strongbox is a simple thing in its conception: in one sense, it’s just an extension of the mailing address we printed in small type on the inside cover of the first issue of the magazine, in 1925, later joined by a phone number (in 1928-it was BRyant 6300) and e-mail address (in 1998). Readers and sources have long sent documents to the magazine and its reporters, from letters of complaint to classified papers. (Joshua Rothman has written about that history and the magazine’s record of investigative journalism.) But, over the years, it’s also become easier to trace the senders, even when they don’t want to be found. Strongbox addresses that; as it’s set up, even we won’t be able to figure out where files sent to us come from. If anyone asks us, we won’t be able to tell them.