What does letterbox friendly mean?Updated 3 months ago Letterbox friendly sizes are based on Royal Mail guidelines: A single 250g bag is sent as a large letter parcel with a maximum height of 25mm. Two 250g bags are sent in packaging designed to fit through most UK letterboxes with a maximum height of 40mm.Mixed orders are sent as a small parcel and will arrive in a larger box that will not fit through a letterbox. Was this article helpful? YesNo