The optional Brother MX-4000 mailbox holds 4 x 100 or 2 x 400 sheets. This mailbox is especially useful when multiple users are accessing the same machine at the same time, as it ensures that printouts are perfectly allocated to each employee. The optional Brother MX-4000 mailbox is compatible with the HL-L6300DW, HL-L6400DW, HL-L6400DWTT and HL-L6400DWTT lockable devices.