You can print on plain paper envelopes in this size:
No. 10 (4.1 × 9.5 inches [105 × 241 mm])
For the WF-7520, you can load No. 10 size envelopes in Cassette 1 only.
Close the output tray, if necessary.
Pull out the paper cassette and remove the paper cassette cover.
Slide the edge guides outward.
Slide the edge guide shown below to your envelope size.
Load envelopes, printable side down, against the edge guide as shown.
Make sure the envelopes are loaded against the edge guide and not sticking out from the end of the cassette.
Slide the edge guides against the envelopes, but not too tight.
Make sure the envelopes fit beneath the top edges of the guide.
To prevent paper feeding problems, make sure you do not load too many envelopes in the cassette.
Gently replace the paper cassette cover and insert the paper cassette.
The envelopes may slide forward slightly as you insert the cassette. This is normal.
Extend the output tray and open the paper stopper.
Always follow these paper loading guidelines:
If you have trouble loading a stack of envelopes, press each envelope flat before loading it or load one envelope at a time.
If print quality declines when printing multiple envelopes, try loading one envelope at a time.
Do not load envelopes that are curled, folded, or too thin.
Paper Loading Capacity