There is disclosed a new and improved envelope processing machine. The machine includes a processing station (54) arranged to present each envelope in an opened condition to an operator in one-by-one relation to facilitate the removal of contents from or the insertion of materials into the envelopes by the operator. A detecting means (70) downstream from the processing station (54) acts upon the envelopes one at a time for sensing a predetermined event corresponding to the suspected absence of complete removal of the contents from or complete insertion of materials into the envelopes. An illumination means (80) actuable in response to the detecting means sensing the predetermined event is arranged to direct light through the envelopes to afford visual verification of the predetermined event by the operator.