Epson All in One Printer User Manual page 25

User's Guide
A
Pull the paper cassette 1 all the way out.
B
Remove the cover.
C
Pinch and slide the edge guides to the sides of the paper cassette.
D
Load envelopes lengthwise with the flap facing up and to the right.
Note:
Make sure the number of envelopes does not exceed the limit.
"Selecting Paper" on page 16
&
Paper and Media Handling
25