Brother MFC-8820DN - Manual (Page 172)

USING THE MFC AS A PRINTER 11 - 15
6
Press and slide the paper-width guide to fit the envelope size.
7
Send the print data to the MFC.
8
After you finish the print job, close the back output tray.
When you put envelopes in the MP tray, please remember the
following;
■
During printing, the inside tray rises to feed envelopes into
the MFC.
■
The side to be printed on must be face up.
■
Put the leading edge (top of the envelope) in first and push
it gently into the tray.