Apple LaserWriter 12/640 PS - Manual (Page 293)

6 When the printer’s Paper Out indicator light flashes, insert the first envelope and slide it
forward until it stops.
Insert the envelope face up (flap down) with the top edge to the right as it
enters the printer.
On a Mac OS computer, if Background Printing is turned on in the Chooser,
a PrintMonitor message prompts you to insert an envelope.
7 If you are printing several envelopes, insert the next envelope when the Paper Out light
flashes again.
Do not feed the next envelope before the light prompts you to, or the
envelope may jam.
Loading labels in the multipurpose tray
You can load one sheet of labels at a time into the multipurpose tray for
manual printing.
Insert the sheet of labels into the paper cassette face up.
IMPORTANT When you print labels, use the multipurpose tray. (This helps
avoid paper jams and curling.)
Don’t attempt to print sheets that
have labels missing. This may cause a jam. Use only labels recommended
for use in laser printers.
268 Chapter 10