See "Printing on Custom-sized Paper Loaded on the Bypass Tray", User Guide
(HTML).
To print in landscape orientation, select the [Rotate by 180 Degrees] check box
on the [Input/Output] tab, and then print.
macOS
• Paper Size: Select the envelope size. If the envelope size is not included
among the options, select [Manage Custom Sizes] and enter the value.
• Paper Type: Envelope
To print in landscape orientation, select [On] for [Rotate by 180 degrees] in
[Basic] in "Feature Sets".
12. Execute printing.
Printing on Envelopes Loaded in the Paper Tray
1. Load an envelope in the Paper Tray.