The Brother MX-4000 4-bin mailbox / sorter / stacker option helps increase control over your Brother printer's output. Assign the four output bins to specific users or group and send print jobs directly to each recipient's bin. When printing large documents, use the bins to increase your machine's output tray capacity. The Brother MX-4000 4-bin mailbox / sorter / stacker option is for use with the Brother HL-EX415DW, HL-EX470W, HL-L6400DW, HL-L6400DWT, HL-L6400DWG, HL-L6400DWX, HL-L9430CDN, and HL-L9470CDN.