Dell 3100cn Color Laser Printer - Manual (Page 204)

3. Insert the print media into the feeder with the recommended print side face up.
4. Slide the width guides until they rest lightly against the edge of the print media stack.
5. Make sure the size and type settings for the multipurpose feeder are set to the correct value for the print media you have loaded.
6. Select print media source, size, and type in your software program and select the print media size and type on the printer operator panel.
Loading Envelopes
NOTE: Do not force the print media.
NOTE: Be careful not to bend the print media.