Epson 1010 User Manual page 68

When manually feeding an envelope, you may have to push it down
slightly while pressing the LOAD/EJECT button to get it to feed
properly.
CAUTION: The printable area for envelopes is shown on
the next page. The print head must not go past the left or
right edge of the envelope or other thick paper. Make sure
that the page setup of your application program keeps the
printing entirely within this printable area.
Paper Handling
2-29