dead letterbox 

A prearranged place for a swap or drop of information or goods. Particularly common usage with Spies or drug dealers.

"The Microfilm was left at the dead letterbox as arranged. We can now release the prisoner."

dead letterbox by Andy 696969 October 17, 2006

dead letterbox 

Where a letter ends up when it is undelieverable, by postal definition, the dead letterbox.

I can't deliever this letter so stick it in the dead letterbox.

dead letterbox by mspenguin November 1, 2006