Canon LBP7100Cn User Manual page 461

<Cause 6> When printing envelopes, the envelopes may crease depending on the type of the
envelopes or the operating environment (especially in a high-humidity environment).
Perform the following procedure in the Printer Status Window.
1. Display the Printer Status Window.
Solution
2.
3. Select the [Perform Envelope Wrinkle Reduction When Printing] check box.
"Printer Status Window"