Canon S400 Reference Manual page 37

Windows
4
Open the Printer Properties dialogue box and select the most appropriate
icon in the Choose Print Mode box under the Main tab. Select Envelope in
the Media Type box. Make sure that the BJ Cartridge Type setting matches
the BJ Cartridge you are using.
Macintosh
4
Select the most appropriate icon that indicates the print mode in the
Printer Properties dialogue box. Specify the media type (Envelope), and
the BJ Cartridge you are using.
Printing on Paper and Other Media
Using Envelopes
37