Dell 1350 Color User Manual page 176

NOTE:
If envelopes are still not fed correctly, add some bending to the flap of the
envelopes as shown in the following illustration.
The amount of the bending shall be 5mm (0.20 inches) or less.
NOTE:
To confirm the correct orientation of each print media such as envelopes,
see the instruction on the Envelope/Paper Setup Navigator on the printer driver.
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