HP Deskjet 6122 Color Inkjet Printer - Manual (Page 16)

Remove the Out tray to load small media other than single envelopes and single
cards.
The Out tray has a slot for single envelope and single card printing.
1. single envelope slot
Flip down the Out tray extension to prevent the paper from falling off the tray.
1. Out tray extension
Raise the Out tray to load most paper sizes.