During Printing - Epson Stylus C41 Series User Manual

3. Load envelopes short edge first with the flap side down, as
shown in the illustration.
Note:
The folding quality and thickness of envelopes vary widely. If the
total thickness of the stack of envelopes exceeds 10 mm, press each
envelope in the stack flat before loading. If print quality declines
when a stack of envelopes is loaded, load one envelope at a time.
Do not use envelopes that are curled or folded.
Flatten the envelope flaps before loading.
Avoid using envelopes that are too thin as they may curl

during printing.

106
Paper Handling