Brother HL-5150D - Manual (Page 121)

TROUBLESHOOTING 6 - 16
Envelope creases
■ Open the face-up (back) output tray and push down the blue tabs at
the left and right hand sides (as shown in the figure below). When you
have finished printing your envelopes, close the face-up output tray to
reset the two blue tabs back to their original position. See page 1-31.
Examples of poor print
quality Recommendation
ABCDEFG
EFGHIJKLMN