Canon MB5400 SERIES Online Manual page 183

3. Slide the front (A) and right (B) paper guides out to make room for the paper.
4. Load the envelopes face-DOWN, centered in cassette 1.
The flap will face up, as shown below.
Up to 10 envelopes can be loaded at once.
Note
• Align the stack of envelopes with the edge of cassette 1 as shown.
Feeding problems may occur if the envelopes are touching the protrusion (C).
183