The letter box has a transparent area (8) in a surface (6) extending perpendicular to a side edge of a letter which has been inserted. The transparent area can be an opening smaller than a letter. The transparent area can be a light-permeable panel at the bottom area of the box. Several transparent areas can be provided on different sides of the box. A letter guide is set in the box to divert incoming letters away from a surface of the box extending parallel to a side edge of an inserted letter.
