Brother MFC-420CN - Manual (Page 140)

11 - 21 TROUBLESHOOTING AND ROUTINE MAINTENANCE
8
Pack the printed materials in the original carton as shown below.
Do not pack the used ink cartridges in the carton.
9
Close the carton.
If you are returning your machine to Brother as part of the
Exchange Service, pack only the MFC. Keep all separate parts
and printed materials to use with your “Exchange” machine.
(For USA) (For Canada)