Canon LBP7210Cdn Manual page 257

CAUTION
Be careful when handling envelopes.
Handle envelopes carefully not to cut your hands with the edges of the envelopes.
Gently load the envelope stack under the load limit guides (A) until it touches the back of
the tray.
Make sure that the paper stack does not exceed the load limit mark lines (B).
CAUTION
Be careful when handling envelopes.
Handle envelopes carefully not to cut your hands with the edges of the envelopes.
IMPORTANT
Loading orientation of envelopes
See the instruction described at
Load envelopes with the front side (non-glued side) facing up.
You cannot print on the reverse side (glued side) of envelopes.
the top of the procedure.