You can load
envelopes in Cassette 2 (lower cassette) as described here. You can
print on plain paper envelopes in this size: No. 10
(4.1 × 9.5 inches [105 × 241 mm])
You can also load a single envelope in the rear paper feed slot,
as described in that section.
Note: Do not
remove or insert the paper cassette during printing.