Epson 1290 Daily Use Manual page 21

Load envelopes flap edge first with the flap side down, as
shown in the illustration.
Do not use envelopes that are curled or folded.
Flatten envelopes before loading.
Avoid using envelopes that are too thin as they may curl
during printing.
Select Plain Paper as the Media Type setting in the printer
software.
Available envelopes sizes are:
No.10, DL, C6, 132 mm 220 mm
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