The Uni-Stacker collects sealed envelopes neatly and can handle up to 1,500 at once (or 3,000 with an extension). This means operators don’t need to empty it as often, giving them more time for other tasks.Used together with the Boxit system, envelopes drop directly into postboxes at the press of a pedal. No lifting, no interruptions—just continuous, ergonomic, and efficient operation.into a mailbox.