Brother MFC-9840CDW User Manual page 144

Examples of poor print
quality
Envelope creases
134
Recommendation
a
Open the back cover.
b
Pull down the two grey levers, one on the left-hand side and one on
the right-hand side to the envelope position, as shown in the
illustration below.
c
Close the back cover and re-send the print job.
Note
When you have finished printing, open the back cover and reset the
two grey levers back to the original position.