Canon BJ-230 - Manual (Page 24)

5. Arrange the stack of envelopes on a firm surface and press down
firmly on the edges to make the folds crisp. Press all the way
around the envelopes to remove any curls and expel air from
inside the envelopes.
6. Align the stack of envelopes with the right edge of the sheet
feeder and slide in the stack until it stops.
7. Adjust the paper guide to the stack of envelopes, and adjust the
paper exit support to match the width of the envelopes.
8. Start your print operation.