Brother HL-3450CN - Manual (Page 67)

CHAPTER 3 BEFORE WORKING WITH THE PRINTER
3-11
Using Envelopes
You will need to attach the Envelope Adapter when you want to print
envelopes.
1. Pull out the Media Cassette and remove the Media Cassette Cover.
2. Attach the Envelope Adapter to
the Media Cassette. Secure the
hooks of the Envelope Adapter
into the Media Cassette.
Fig. 3-2
3. Adjust the Envelope Guide to the
size of the envelopes you want to
load.
Fig. 3-3