The Mixed Mail Problem

A generic parcel sorter handles thick, rigid items well and thin flexible items poorly. Letter mail is the opposite challenge: items are thin, light, easily creased, and arrive in wildly varying stiffness. A 3 g airmail envelope and a 400 g glossy catalogue must both be transported at speed without jamming, skewing or damaging - and both must be read reliably.

The result is that letter and flat sorting demands purpose-built transport: friction feeders instead of belt induction, pinch-belt or vacuum transport instead of slat beds, and divert gates rather than shoes or tilt trays. Every mechanical choice in the machine is optimised for thin flexible media.

Letter and flat mail sorting system - purpose-built transport for thin, flexible mail media.

System Architecture: From Feeder to Bin

1. Automatic Feeding and Singulation

Mail is loaded in bulk stacks. A friction or vacuum feeder separates one item at a time, with double-feed detection to catch stuck envelopes. Feeder tuning is the highest-leverage adjustment in the entire machine: a feeder set correctly for the current mail mix eliminates the majority of jams before they occur.

2. Imaging and Address Recognition

Each item passes an imaging station that captures the address face. OCR resolves the printed address; where handwriting or poor print defeats OCR, the image is routed to a video coding workstation where an operator keys the missing fields in seconds. Barcode and postal code symbologies are read in the same pass, which is far faster than OCR when a machine-readable mark is present.

3. Destination Lookup and Divert

The recognised address is matched against the delivery point database to yield a sort bin. The control system tracks the item through the transport path and fires the divert gate at the calculated moment. Items that cannot be resolved are routed to a reject bin for manual handling rather than being force-sorted.

4. Multi-Pass Sequencing

Delivery point sequencing - putting mail into the exact order a carrier walks a route - normally requires two passes. The first pass sorts to route level; the second re-feeds the output and sorts within each route to walk order. This doubles the machine cycles per item but removes the single most labour-intensive task in the delivery office.

Indicative Technical Specification

Specifications are indicative and configured per project. Actual throughput depends on mail mix, thickness distribution and read rate.

Feeder and transport section - correct feeder tuning is the highest-leverage adjustment for jam-free running.

Operational Metrics That Actually Matter

Buyers frequently compare machines on headline throughput alone. In live postal operations, three other metrics predict total cost far more reliably.

• Read rate - the percentage of items whose address resolves automatically. Each percentage point of read rate improvement removes a measurable amount of video coding labour across a year.
• Jam rate per thousand items - jams cost far more than the clearance time, because they interrupt flow and force partial re-feeds. A low jam rate on your mail mix matters more than a low rate on a demonstration stack.
• Effective throughput - rated speed multiplied by realistic uptime. A 40,000 iph machine running at 70% availability is slower than a 30,000 iph machine at 95%.

When evaluating suppliers, request these figures measured on a sample of your own mail rather than on standardised test media. The difference between catalogue figures and real-mix performance is frequently substantial.

Where Mail Sorting Automation Is Heading

Three trends are reshaping specification decisions. First, hybrid mail and parcel streams: as small e-commerce items increasingly arrive in polybags, mail sorters are being specified with wider thickness tolerance to absorb them. Second, deeper track-and-trace: customers now expect item-level visibility on letter mail, which pushes imaging and data capture requirements upward. Third, energy and footprint efficiency, as urban sorting centres face rising space and power costs.

Output stacker section - bin configuration is matched to the operator's route structure.

Frequently Asked Questions