You can print on plain paper envelopes in this size:
No. 10 (4.1 × 9.5 inches [105 × 241 mm])
Flip the feeder guard forward.
Pull up the paper support and its extension.
Pull out the output tray and open the paper stopper on the end.
Slide the edge guide left.
Load up to 10 envelopes against the right side. Load them printable side up and flap edge left.
Slide the edge guide against the envelopes, but not too tightly.
Flip the feeder guard back.
If you have trouble loading a stack of envelopes, press each envelope flat before loading it or load one envelope at a time.