Epson FX-1050 User Manual page 48

You can also feed envelopes with the optional cut sheet feeder. See the
section on the cut sheet feeder in Chapter 7. before loading envelopes
into the cut sheet feeder, you need to adjust the paper thickness lever. See
the table showing envelope types and recommended lever positions on
page 2-18.
WARNING: When printing on envelopes, be sure that your
application program settings keep the printing entirely within
the printable area of the envelopes as shown below.
To make sure that the printing fits within this area, always
print a test on a single sheet of paper before printing on
envelopes.
2-20 Paper Handling