Mechanical sorting is suitable for items meeting the requirements set for dimensions, weight, shape, colour and contents of machine sortable items. The recipient's address must be printed on the envelope or visible inside a window-panel envelope.
Items may not contain any hard or inflexible objects such as paper clips, keys or casings. Only sealed envelopes or cards can be sorted mechanically. Mechanically sortable items are posted packed in boxes, large items separate from small ones, with the address information showing in the same direction.
Address Markings of Machine-Sortable Letters
The design and markings of machine-sortable envelopes are determined based on whether the address information is on a label, visible through a window-panel or printed directly onto the envelope.
Further information is available in the Guide to planning machine-handled items (pdf).