Epson CX6500 Reference Manual page 136

Note:
You can load up to 10 envelopes at a time in the sheet feeder.
Set the feeder guard
back.
Return adjust lever to the standard
envelopes.
Note:
If you are going to print a large number of envelopes, first try printing one sheet to
confirm that it can be printed properly. You can then print the rest of the sheets.
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.
position after printing