Canon PIXM MX300 Series User Manual page 30

Up to 10 envelopes can be loaded at once.
Pinch the Paper Guide and slide it against the left side of the envelope.
(2)
Set the Paper Thickness Lever to the right.
(3)
Note
Reset the Paper Thickness Lever to the left when you finish printing.
See The position of the Paper Thickness
3
Specify the settings in the printer driver.
Select Envelope in Media Type.
(1)
Select the size for envelopes.
(2)
In Windows, select DL Env. or Comm. Env. #10 in Page Size.
In Macintosh, select DL Envelope or #10 Envelope in Paper Size.
Select Landscape in Orientation.
(3)
Important
Be sure to set the printer driver setting properly. If you do not, the address
will be printed in the wrong direction.
Note
For details on printer driver settings, see
with Macintosh.
Lever.
Printing with Windows
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or Printing