Envelope width, thickness, flap position, paper strength, contents, window material, and edge condition can all affect feeding. Bent corners and overfilled envelopes may enter unevenly, while glossy or heavily textured stock can behave differently from ordinary business envelopes. Confirm the machine’s supported size and thickness range before purchase. If the office receives several envelope formats, test representative samples rather than relying on one standard size. Mail should also be inspected for clips, staples, rigid inserts, or damaged sections that could interfere with the opening mechanism.