HP LaserJet Enterprise 600 Printer M603 series - Manual (Page 205)

Clear jams from the optional envelope feeder
This procedure applies only to jams that occur when you are using an optional envelope feeder.
1. Remove any envelopes that are loaded in the
optional envelope feeder. Lower the envelope
weight and lift the tray extension up, to the
closed position.
2. Grasp both sides of the optional envelope
feeder and carefully pull it out of the product.
3. Slowly remove any jammed envelopes from
the optional envelope feeder.
4. Slowly remove any jammed envelopes from
the product.
ENWW Clear jams 189