Canon MG7100 series Online Manual page 129

(4) Align the paper guide
(5) Slide the paper guide
with both sides of the envelopes.
Do not slide the paper guides too hard against the envelopes. The envelopes may
not be fed properly.
Note
Do not load envelopes higher than the load limit mark (F).
Keep the envelope stack height below tabs
(6) Insert the cassette (lower) into the machine.
Push the cassette (lower) into the machine until it stops.
(A) in front with the envelopes.
(B) on the right to align the right and left guides
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(G) of the paper guides.