HP LaserJet 9000 Printer series - Manual (Page 53)

5 Printing 53
Orienting media
Type of media Tray Duplexed Orient media like this
Labels, Letter, A4 size
sheets, or transparencies Tray 1 only No
(Never duplex) Long edge toward feed direction; side to be printed
facing up.
Type of media Tray Duplexed Orient media like this
Envelopes Tray 1 only No
(Never duplex) Short edge toward feed direction; side to be printed
facing up. If height of envelope is greater than
7.5 inches, feed flap first. Otherwise, feed flap toward
rear of product.