Envelopes can be printed only from tray 1. Set the tray media size to the specific envelope size. See Printing envelopes from tray 1.
Adhere to the following guidelines to help ensure proper printing on envelopes and to help prevent printer jams:
In high humidity environments, envelopes should be printed long-edge first to prevent them from sealing during printing. For long-edge printing, envelopes should be loaded long edge first, face down. See Printing envelopes from tray 1.