Canon imageRUNNER 3530 Reference Manual page 321

9
Loosen the two screws fixing the back width guide of the
envelope feeder attachment.
10
Press down on the envelope receptacle, and move the back
width guide to align it with the mark for the desired envelope
size.
11
Fix the back width guide in place with the screws.
Envelope Feeder Attachment-C1 (Optional)
7
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