Brother HL-3450CN - Manual (Page 70)

CHAPTER 3 BEFORE WORKING WITH THE PRINTER
3-14
Before loading envelopes in the cassette, check the following:
• Envelopes should have a lengthwise sealing flap.
• The sealing flaps should be folded crisply and correctly (irregularly cut
or folded envelopes may cause paper jams).
• Envelopes should consist of two layers of paper in the following
marked area.
Fig. 3-6
• Envelope joints that are sealed by the manufacturer should be secure.
• All sides should be properly folded without any wrinkles or creases.
• Print quality may vary between different style envelopes. It is a good
idea to test the envelopes you wish to use prior to purchasing large
quantities.