The largest mailbox measures 68.484 m³ (2,418.49 ft³) and was created by Yamaguchi University Choshu Enjoying Science Innovation Project (Japan). It was presented and measured at Yamaguchi University in Ube, Yamaguchi, Japan, on 27 December 2012.

The large mailbox is a replica of a commonly used red Japanese mailbox made of iron. A student from Yamaguchi University who was involved in this attempt posted a letter to his mother using this mailbox, and the letter was collected by a postal worker to be delivered to the intended receiver.