postalref

Mail processing: how USPS sorts and moves mail

Inside USPS, processing plants sort mail in phases, first toward its destination and then down to a carrier's route, and a carrier delivers it. Mail moves between plants on dispatches timed to meet service standards, USPS's delivery goals for each class, usually counted in days.

Updated November 6, 2026100 sources

Questions

What does processed through USPS sort facility mean?

It means USPS sorted the package in the plant named in the scan by its city, state and ZIP Code. A package can get several of these scans, but tracking shows only the first and last at each plant on a calendar day.

What does arrived at USPS regional facility mean?

It is a trailer arrival scan: the package was in a container scanned as arriving at a USPS facility. USPS adds regional to the wording for some facilities, and Departed USPS Regional Facility means the container was scanned as loaded onto transportation. A sort inside the facility shows in tracking as Arrived at USPS Facility or Processing at USPS Facility. Mail with a wrong barcode or ZIP Code can be sent to the same wrong destination again and again, which USPS calls loop mail.

What does in transit to next facility mean on USPS tracking?

It means the package is moving within the USPS network to its next facility, and tracking shows the event to fill a visibility gap. Product Tracking and Reporting shows this wording when it has no expected delivery date stored, and In Transit, Arriving Late when the package looks late. When a delay hits a place the package is leaving or heading to, tracking can show a Processing Exception for transportation problems (TX), weather (WX), or emergency or other conditions (OX). USPS is retiring event NT in PTR2, the platform that runs beside Product Tracking and Reporting until customers migrate to it.

Why is USPS taking so long to deliver packages?

A package can run late when transportation problems, weather or an emergency delay a place it is leaving or heading to, which tracking shows as a Processing Exception. Mail can also be misrouted, sent from its origin plant to the wrong destination plant. In February 2021, USPS's Office of Inspector General found that misrouted mail has a high risk of missing its service standards. Tracking also shows when USPS sends a package to the right delivery unit after routing it wrongly, or when a shipper's agent drops it at the wrong USPS facility.

How long does it take for Priority Mail Express to arrive?

Priority Mail Express comes with a money-back guarantee for next-day or second-day delivery in most cases. Delivery on a Sunday or a federal holiday is available on request, for an additional charge.

Why is USPS Certified Mail taking so long?

Certified Mail gets no faster handling: USPS dispatches and handles it in transit as ordinary mail. It is available only for mail paid at First-Class Mail or Priority Mail prices.

How does USPS sort mail for delivery?

USPS sorts mail in phases: the origin plant cancels it and sorts it by destination, then the destination plant sorts it to carrier routes. For letters, the last sorts put the mail into the carrier's walk sequence in two passes. Mail tracking numbers these phases, and the higher the number, the closer the mail is to delivery.

How does USPS deliver mail across the country?

USPS moves mail in three legs: from collection to the origin plant, from the origin plant to the destination plant, and from the destination plant to delivery. The origin plant sorts mail toward its destination, the destination plant sorts it to carrier routes, and carriers at a delivery unit deliver it. Since July 2025, USPS has set service standards by 5-digit ZIP Code pairs, which it says reflect the three legs more accurately than First-Class Mail's old plant-to-plant driving distances.

How is USPS mail transported?

Mostly over highways: as of September 2025, USPS relied on contractors on highway contract routes for the significant majority of long-haul transportation between its facilities. Those routes range from long-haul tractor trailers to box delivery routes. USPS owns no aircraft and relies on third parties to carry mail and packages by air, in the U.S. and abroad. It said its service standard changes helped it shift package volume from air to highway where that cost less.

How can I estimate USPS delivery time by ZIP Code?

The USPS Service Standards API returns delivery standards or estimated delivery dates for package mail classes from an origin and a destination ZIP Code. USPS also publishes service standard files in days by 3-digit origin, destination and product, and an API that answers for one 5-digit pair.

What should I do for a customer who is not receiving their newspaper with approved exceptional dispatch daily?

Start with the postmaster at the Post Office that serves the customer. If that does not resolve it, contact a Business Service Network representative or USPS Customer Service at (800) 275-8777. Exceptional dispatch is a publisher's own delivery of Periodicals copies to a Post Office other than its entry office.

How it fits together

Mail travels through processing plants, central facilities that sort and dispatch incoming and outgoing mail for a service area. Collection mail and mail from business mail entry units get their first sort in an outgoing primary operation, toward area distribution centers, plants and states. With destination entry, a mailer who carries mail to a postal facility pays a lower price, generally lower the closer it is to delivery.

USPS splits the trip into three legs: collection to origin processing, origin processing to destination processing, and destination processing to delivery. As of December 2025, Regional Processing and Distribution Centers gathered, sorted and dispatched mail and packages to and from the network for large regions. Local Processing Centers, mid-sized plants, sorted them mainly to the Post Offices that deliver them. Sorting and Delivery Centers were large delivery hubs with package sorting equipment and many carriers, connected to smaller delivery units, the local Post Offices whose carriers collect and deliver mail.

Each plant sorts mail in operations grouped into numbered phases, from cancellation at the origin to the final sorts at the destination. Machines sort mail by reading the address or a barcode on each piece. USPS combines residual mail, the pieces left after a mailer's presort, with other residual mail to get enough volume to process.

Between plants, mail moves on dispatches, and the day's last one that still meets the service standard is the dispatch of value. At the end, carriers at a delivery unit take the mail out on their routes, and machines can sort it into delivery order first.

Service standards set how many days each class should take from entry to delivery. USPS measures service performance as the days from entry by the mailer to delivery by USPS. A package's scans at each plant show in package tracking.

Processing plants

A processing and distribution center is a central mail facility that sorts and dispatches incoming and outgoing mail for a service area. It is usually a general mail facility or a sectional center facility, the plant for Post Offices whose ZIP Codes share their first three digits. Area Mail Processing moves the sorting of several Post Offices or facilities into other automated plants. As of April 2025, USPS processed mail at more than 300 mail processing facilities.

An area distribution center receives and distributes mail for a range of ZIP Codes, as one point in the national distribution network. An automated area distribution center is an automated plant that does the same work.

A network distribution center is a highly mechanized plant, formerly called a bulk mail center. As of July 2013, USPS classed network distribution centers in three tiers. Tier 1 sites distributed local and destination mail, Tier 2 sites also distributed it to the network, and Tier 3 sites also consolidated less-than-truckload volumes. By September 2026, USPS said network distribution centers still do significant processing, particularly for parcels, but no longer have a distinct network role. An auxiliary service facility is a satellite hub for one network distribution center, usually part of a processing and distribution center.

As of March 2024, USPS was replacing its legacy network of processing and distribution centers and network distribution centers with two standard kinds of plant. A Regional Processing and Distribution Center is meant to handle a region's outgoing letters, flats and packages and its incoming packages. It is also meant to be the region's control point, managing the mail and packages that enter or leave it. A Local Processing Center is meant to sort incoming letters and flats for its 3-digit ZIP Codes and collect packages bound for delivery. USPS expected to open about 60 Regional Processing and Distribution Centers.

The Shipping Services File is the electronic file that holds a shipper's manifest and payment information. In it, a destination entry package's destination rate indicator gives the type of facility where it is entered. One of its codes covers entry at a network distribution center or a Regional Processing and Distribution Center. Another covers sectional center facilities, Local Processing Centers for mail and Regional Processing and Distribution Centers for packages.

A service hub cross-docks mail that mailers prepare and enter there, then carries it to the delivery units it serves. An International Service Center dispatches and receives international mail.

Area Distribution Center

Also called ADC

“A mail processing facility that receives and distributes mail destined for specific ZIP Code ranges. An ADC is one of the points within the national distribution network as is defined by the first three digits of the ZIP Code of the Post Offices it serves”

Auxiliary Service Facility

Also called ASF

“A mechanized facility, usually part of a processing and distribution center (PDC), that has its own service area and serves as a satellite processing hub for a particular network distribution center (NDC).”

Network Distribution Center

Also called NDC

“A highly mechanized and automated mail processing facility formerly designated as a bulk mail center.”

Sectional Center Facility

Also called SCF, Sectional Center Facilities, section center facility

“A postal facility that serves as the processing and distribution center (P&DC) for Post Offices in a designated geographic area as defined by the first three digits of the ZIP Codes of those offices.”

Processing and Distribution Center

Also called P&DC

“A central mail facility that distributes and dispatches part or all of both incoming mail and outgoing mail for a designated service area.”

Automated Area Distribution Center

Also called AADC

“An automated mail processing facility that receives and distributes mail destined for specific ZIP Code ranges. An AADC is one of the points within the national distribution network as defined by the first three digits of the ZIP Code of the Post Offices it serves.”

International Service Center

Also called ISC, exchange office

“A facility that dispatches and receives international mail going to and received from designated operators.”

Sorting operations

Mail processing is the group of steps that sort mail and ready it for dispatch and delivery. Before any sorting, culling removes parcels and odd-shaped pieces from letter mail, and the letters are faced and canceled. Each sort follows a scheme, a plan usually based on ZIP Codes and the network of plants.

USPS numbers the phases of mail processing from 0 to 4, and the higher the number, the closer the mail is to delivery.

  • Phase 0: origin processing starts with cancellation of the postage on collection mail.
  • Phase 1: origin processing goes on with outgoing primary and outgoing secondary sorts.
  • Phase 2: destination processing sorts the mail in incoming primary, managed mail or incoming SCF operations.
  • Phase 3: destination processing ends with incoming secondary, box section, delivery point sequence or sector/segment sorts.
  • Phase 4: the delivery unit's events make up the last phase.

Outgoing primary separates originating mail by automated area distribution center and by 3-digit and 5-digit ZIP Code. Outgoing secondary sorts the mail that outgoing primary did not finish. Managed mail sorts outgoing primary mail from automated area distribution center level down to 3-digit ZIP Codes.

At the destination, incoming primary separates local mail by 5-digit ZIP Code. Incoming secondary separates it by carrier route. For flats, incoming secondary is the last expected sort. A box section sort separates local mail by Post Office Box section. A sector/segment sort separates mail by ZIP+4 sector in a first pass, then by ZIP+4 segment in a second.

Residual mail is what remains after a mailer's presort, too little to prepare for one destination. Containers labeled MXD hold mixed mail for several destinations. It is generally residual mail, which USPS combines with other residual mail to get enough volume to process and dispatch.

outgoing primary

Also called Outgoing (O/G) Primary

“Processing of originating mail separated by Automated Area Distribution Center (AADC), 3-digit ZIP Code separations, and 5-digit ZIP Code separations for overnight, 2-day, and 3-day delivery. Additional processing is expected on automated equipment.”

Outgoing Secondary

Also called Outgoing (O/G) Secondary

“Processing of originating mail not finalized on outgoing primary separated by AADC, 3-digit ZIP Code separations, and 5-digit ZIP Code separations for overnight, 2-day, and 3-day delivery. Additional processing is expected on automated equipment.”

Managed Mail

“Processing of 3- and 5-digit outgoing primary mail normally sorted from an AADC level down to 3-digit ZIP Code level, with high-volume 5-digit zones and firms also held out.”

Incoming (I/C) SCF

“Processing of local destinating mail normally separated by the host SCF by 5-digit ZIP Code.”

Incoming Primary

Also called IP, Incoming (I/C) Primary

“Processing of local mail normally separated by the host SCF by 5-digit ZIP Code for which it has delivery responsibility.”

incoming secondary

Also called IS, Incoming (I/C) Secondary

“Processing of local mail normally separated by carrier route.”

mail processing

Also called processing

“An integrated group of subfunctions required to sort and distribute mail for dispatch and eventual delivery. The principal subfunctions are culling, edging and stacking, facing and canceling, sorting, tying, pouching, bundling, sacking, and traying.”

cull

“(1) To remove nonletter mail (such as small parcels, rolls, and odd-shaped material) from letter mail (and nonmachinable mailpieces from machinable and automation pieces) by hand or machine. During culling, specials (such as accountable mail) and flats are segregated from other letter mailpieces. (2) To remove mail from containers such as sacks or trays for the first time before it enters the mailstream.”

residual mail

“Mailpieces remaining after completion of a presort sequence.”

Sorting equipment

Mail processing equipment is the machinery USPS sorts with, from automated machines to manual cases.

For letters, a facer-canceler turns each piece the same way and cancels its stamps. As of July 2013, the Advanced Facer Canceler System 200 faced and canceled collection mail, read barcodes on prebarcoded mail, and printed a POSTNET barcode on mail without one. It added image-based indicia detection and a two-tier 12-bin stacker module to the older Advanced Facer Canceler System with Optical Character Reader. An optical character reader reads the address and sprays the ZIP Code onto the piece as a barcode. A barcode sorter then sorts letters by reading that barcode. It has a mail feed, a barcode reader and stackers that sort into many separations.

The Delivery Barcode Sorter sorts letters that already carry a barcode, printed by the mailer or by USPS equipment. Intelligent Mail barcodes are among the barcodes used for postal processing. The Delivery Barcode Sorter can sort letters into carrier walk sequence, so the delivery unit does not sort them again. Some carry modules that process undeliverable letters for the Postal Automated Redirection System.

For flats, the Automated Flats Sorting Machine 100 is a fully automated sorter. It takes mail from automatic feeders, processes it with optical character recognition, and captures images of script and typed mail for video encoding. Images of flats whose addresses it cannot resolve go to an off-site remote encoding center, which sends the results back in real time. A take-away conveyor carries its trays off and can be adapted to robotic handling or to feed a Tray Management System. A Tray Management System moves trays of mail around a plant automatically.

The Upgraded Flats Sorting Machine 1000 took pieces too large for the Automated Flats Sorting Machine 100, and could also sort mail without barcodes. The Flats Sequencing System sorted flats into delivery order in two passes and sent them to delivery units in street trays. By September 2026, USPS had discontinued its flats operations on both machines.

The Automated Parcel and Bundle Sorter sorts small parcels and bundles of letters and flats, with barcode and optical character reader technology. It was called the Small Parcel and Bundle Sorter until USPS upgraded and renamed it in 2011. As of July 2013, the parcel sorting machine was a carrousel about 1,600 feet long, whose 120 chutes fed conveyor belts to truck docks, slides or other sorters. It sorted parcels to separations that typically included other network distribution centers and high-volume facilities.

Mail service providers run multiline optical character readers of their own, which barcode and presort mail so its owner gets automation discounts.

Bar Code Sorter

Also called BCS

“A computerized machine that sorts letter-size mail by using a barcode reader to interpret an imprinted barcode.”

Delivery Barcode Sorter

Also called DBCS

“An automated letter sorting machine that is used for letter-size mail already barcoded either by mailers or by USPS on other mail processing equipment.”

Optical Character Reader

Also called OCR, Optical Character Recognition

“An automated mail sorting machine that interprets the address information on a mailpiece and sprays the corresponding ZIP Code information onto the piece as a barcode.”

Advanced Facer-Canceler System

Also called AFCS

“A machine with many components that culls, faces, and cancels through a series of automated operations First-Class Mail lettersize pieces received primarily from collection mail.”

Automated Flat Sorting Machine

Also called AFSM, AFSM100, Automated Flats Sorting Machine, Automated Flats Sorting Machine 100

“A fully automated machine that processes flatsize mail.”

Automated Parcel and Bundle Sorter

Also called APBS

“An upgraded Small Parcel and Bundle Sorter with a new control system, barcode and optical character reader technology, and improved induction stations.”

Tray Management System

Also called TMS

“A transportation and information system that automates the movement of trays of mail within a plant.”

Transportation between plants

Mail moves between operations and plants on dispatches, mail readied and loaded for transportation. The dispatch of value is the day's last dispatch that still meets the service standard for the class or destination. Clearance time is the latest time mail can pass through an operation and still make its dispatch. The last chance dispatch is the final transportation from the origin that reaches the destination in time.

For a mailer, the critical entry time is the latest time mail can arrive to be processed and dispatched within service standards. Under exceptional dispatch, a Periodicals publisher carries copies to other Post Offices itself, to improve delivery time.

Highway contract routes, run by contractors who carry mail in bulk between postal points, are USPS's largest group of transportation services. They range from long-haul tractor trailers to box delivery routes, though they generally do not deliver to individual addresses along the way. Contract routes that deliver and collect mail for individual customers are also called contract delivery service routes. The National Air and Surface System produces the dispatch and labeling information for all mail classes.

As of September 2025, USPS neither owns nor operates aircraft, and relies on third parties for air transportation in the U.S. and abroad. Airlift is the movement of mail by air taxi operators and air carriers. Intermodal transportation uses two or more modes to move mail from origin to destination. Interline movement carries mail on the connecting schedules of more than one air, highway or rail carrier.

Cross-docking moves mail through a facility without processing it there. The mail goes straight between vehicles, or through a staging area. A surface transfer center consolidates mail to fill its vehicles, cross-docking containers and sorting mixed mail for dispatch.

Scan events a package gets as it leaves a Post Office and as it arrives at, is sorted in and leaves USPS plants.

PTR Domestic Scan Events, October 2026
EventUSPS.com wordingWhat it means
10Arrived at USPS Facility or Processing at USPS FacilityThe item was sorted in the processing facility indicated by the city, state and ZIP Code. Depending on the class of mail, or origin and destination of the parcel, customers may see more than one of these events, but only the first / last such scan at each site on a calendar day; others are suppressed. Note that on USPS internal sites the event is referred to as "Enroute / Processed".
A1Arrived at USPS FacilityThis is a trailer arrival event, meaning that the item was nested to a container that was scanned as arriving at a USPS facility. The term "regional" may sometimes be included in the language for some facilities.
EFDeparted USPS FacilitySortation process at the distribution facility is complete; the item is being dispatched on the next available transportation to the next processing facility or the destination delivery unit
L1Departed USPS FacilityThe item is nested to a container that was scanned as being loaded onto transportation at a USPS facility. The term "regional" may sometimes be included in the language for some facilities.
SFDeparted Post OfficeArticles receiving an Acceptance scan at the retail window or by a carrier have left the local Post Office and are enroute to the first USPS processing facility.
T1Departed USPS FacilityThe item is nested to a container that was scanned as having departed a USPS facility.
U1Arrived at USPS Facility Note, earliest U1 only: USPS in possession of itemThis event indicates that the package within a container was unloaded from a truck.

7 codes in the PTR Domestic Scan Events, October 2026, where Event is SF or U1 or A1 or 10 or EF or L1 or T1 and Status category is In Transit.

USPS is retiring event EF, Departed USPS Facility, across all tracking channels as it moves tracking to PTR2.

National Air and Surface System

Also called NASS

“A computerized system operated at the St. Louis Accounting Service Center and distribution networks offices to produce dispatch and labeling information for all mail classes.”

cross-docking

“A dock transfer that entails transporting mail that has not and will not be processed in the facility. Mail or equipment may be transported directly between two vehicles, between a vehicle and a staging area, or between two staging areas. The staging areas may be on the platform or inside the facility.”

dispatch

“(1) Mail readied and loaded for transportation. (2) To ready the mail for loading. (3) The act of labeling, containerizing, and moving mail between operations within a facility or from an operation to the platform area for eventual transport on designated routings to other facilities.”

dispatch of value

Also called DOV

“The last dispatch of the day that is loaded on transportation in time to meet the service standard for the mail class or destination.”

clearance time

Also called CT

“The latest time that a type of mail (either class or destination) can pass through an operation to make the proper dispatch to the downline operation or facility by the critical entry time of that operation or facility.”

last chance dispatch

“The final transportation leaving the origin office that can deliver mail to the destination facility in time to make the service standard commitment (i.e., at or before the critical entry time of the destinating facility.)”

highway contract route

Also called HCR, HC

“A route of travel served by a postal contractor to carry mail in bulk over highways between designated points. HCRs generally do not deliver mail to individual customer addresses along the line of travel. Highway contract routes make up the largest single group of transportation services used by USPS and range from long-haul tractor trailers to box delivery routes. (Formerly called star route.)”

surface transfer center

Also called STC

“A mail consolidation and redistribution facility with the primary function of achieving increased vehicle cubic capacity and utilization. STCs receive mail containerized by product type or by ZIP Code range for cross-dock transfer; with mixed mail volume sorted for dispatch to the appropriate destination.”

Delivery

A delivery unit is a Post Office, station, branch or carrier annex with carriers who deliver mail. Each carrier serves a carrier route, the addresses one carrier delivers to. Routes include city routes, rural routes and Post Office Box sections.

A city carrier cases, delivers and collects mail along a city route, walking or driving. A rural carrier does the same by vehicle along a rural route. The rural carrier generally furnishes the vehicle.

To case mail is to sort it by hand into a case, a frame of labeled separations. Delivery point sequence sorts letters by machine into delivery order, so carriers do not sort them by hand before leaving. Walk sequence is the order in which a carrier delivers a route.

USPS can deliver to the occupants of an apartment or office building at one central point, which it calls centralized mail delivery. A cluster box unit is one such point: a group of individually locked compartments, such as a wall-mounted unit in an apartment building. The carrier can generally open all its compartments at once with a special key.

The law requires USPS to run an integrated network that delivers mail and packages at least six days a week. Carriers deliver some packages on Sundays, such as Priority Mail Express for an extra charge and USPS Connect Local for a fee where available. As of September 2025, USPS's normal Sunday delivery included Priority Mail Express and same-day package delivery through its hub-and-spoke structures. A package that arrives at its Post Office before 9:30 am is usually delivered that day, and one that arrives later, the next business day.

delivery unit

“A Post Office, Post Office station, or Post Office branch or other facility such as a carrier annex that has carrier mail delivery functions.”

Carrier Route

Also called CR, Carrier Route Identifier, Carrier Route Id

“(1) The addresses to which a carrier delivers mail. In common usage, carrier route includes city routes, rural routes, highway contract routes, Post Office Box sections, and general delivery units. (2) A presort level in which all pieces in the bundle or container are addressed for delivery to the same city route, rural route, highway contract route, Post Office Box section, or general delivery unit. (3) A price category available for some mail classes or products prepared at a carrier route presort level.”

city carrier

“An employee who cases, delivers, and collects all mail classes along a city route by walking or driving to residences and businesses within an area authorized for city delivery service.”

rural carrier

“An employee assigned to case, deliver, and collect mail using a vehicle along a rural route and to provide most services available at a small Post Office. The rural carrier generally furnishes the vehicle and equipment for handling the mail, receiving Equipment Maintenance Allowance.”

case

Also called flats case, letter case

“(1) A piece of equipment that contains labeled separations into which clerks or carriers manually sort letters, flats, or irregular parcels. Cases are designed to allow flexible configuration of the separations, and they can be expanded by attaching additional cases (wing cases) on either side. (2) To sort mail into a case. To place letter and flat mail into the separations of a carrier case. (3) To place flat mail in delivery sequence outside a case using the delivery order shown for the letter mail.”

delivery point sequence

Also called DPS

“(1) The arrangement of mail into delivery order by using the delivery point code and other data elements. (2) An automated process of sorting mail by carrier routes into delivery order, eliminating the need for carriers to sort the mail manually in the delivery unit prior to their departure to the routes. (3) The sort plan or scheme in which letter mail is sorted to walk sequence for carrier routes using barcode sorting equipment such as the delivery bar code sorter. Depending on the barcode sorting equipment, DPS typically entails two or three passes to reach walk sequence order. (4) To sort mail into delivery order using this automated process.”

walk sequence

“The order in which a carrier delivers mail for a route. This order is required for most carrier route presort mail.”

Service standards

Service standards are USPS's stated delivery goals for each mail class and product, usually counted in days from entry to delivery. They include destination entry standards for mail entered at or near its destination facility. Alaska, Hawaii and territories such as Guam have a separate set.

USPS first published modern service standards in January 2007, as the Postal Accountability and Enhancement Act of 2006 required. It posts them publicly and updates them as its processing, transportation and delivery network changes. The July 2025 Service Standards Preview gives the file layouts for changes that support the network changes in Delivering for America, USPS's strategic plan.

USPS publishes the standards as files of days by 3-digit origin, 3-digit destination and product, with a 5-digit supplemental file. An API answers for one 5-digit pair and one product or all products. Inside USPS, the Service Delivery Calculator gives systems the service standards and expected delivery dates.

These service standards for First-Class Mail, USPS Marketing Mail and Package Services took effect on July 1, 2025.

  • First-Class Mail standards range from 1 to 5 days, apart from USPS Connect Local, which has a 0- to 1-day standard.
  • Eligible Presort First-Class Mail accepted at a Local Processing Center, for delivery in that center's own area, has a 1-day standard.
  • USPS Marketing Mail mailed end to end within the contiguous 48 states has a 4- to 7-day standard, which replaced a 3- to 10-day one.
  • USPS Marketing Mail at a destination Regional Processing and Distribution Center rate has a 5-day standard within the contiguous 48 states.
  • Package Services, which include Media Mail and Bound Printed Matter, have a 4- to 7-day standard end to end within the contiguous 48 states.
  • Package Services at a destination delivery unit rate have a 1-day standard.

As of September 2025, Priority Mail Express offers overnight to 2-day delivery to most U.S. destinations, with a money-back guarantee. Priority Mail's delivery day is specified but not guaranteed. USPS lists 1 to 3 days for returns shipped with Priority Mail.

USPS Ground Advantage replaced First-Class Package Service, Parcel Select Ground and USPS Retail Ground in July 2023. As of September 2025, it has 2- to 5-day service standards for packages up to 70 pounds. Its delivery day across the continental U.S. is specified but not guaranteed.

As of January 2026, Priority Mail Express International goes to about 180 countries and reaches many major markets in 3 to 5 business days. Priority Mail International reaches many major markets in 6 to 10 business days. For both, the actual days vary with origin, destination and customs delays.

The clock starts on Day Zero, the date a piece enters the mailstream. Overnight mail, received by the critical entry time, is expected to be delivered the next day. It is the highest priority of outgoing mail in a plant.

service standards

“Stated delivery performance goals for each mail class and product that are usually measured by days for the period of time taken by USPS to handle the mail from end-to-end (that is, from the point of entry into the mailstream to delivery to the final destination). Established service standards also include destination entry standards for mail entered by the mailer at or near a postal destination facility. A separate set of standards is established for noncontiguous states such as Alaska and Hawaii and territories such as American Samoa and Guam.”

July 2025 Service Standards Preview

“The technical documentation provided here will outline the future file layouts to assist customers in preparing their systems for these changes.”

modern service standards

“States goals for service achievement for each mail class first published in January 2007 in accordance with the requirements of the Postal Accountability and Enhancement Act of 2006. The standards are publicly posted and updated periodically to reflect changes in the processing, transportation, and delivery network.”

Day Zero

Also called D-0

“The date when a mailpiece enters the mailstream and the date when the clock starts for purposes of service performance measurement.”

overnight

“A designation for a dispatch of value in which delivery is expected the day after mail is received by the critical entry time. This dispatch is considered the highest priority of outgoing mail in processing facilities.”

Service Delivery Calculator

Also called SDC

“A Web service that provides service standards to USPS systems as well as the commitment and expected delivery dates. An offline (local) option, called Service Delivery Calculator-Lite, is available for Point of Service One (POS ONE) and Automated Postal Center (APC) terminals to receive service standard responses when the SDC Web service is unreachable.”

What goes wrong

  • Missent mail is mail USPS did not dispatch by its official schemes or schedules, such as mail for Tampa received in San Francisco. USPS sends a missent package to the right delivery unit on the next dispatch, as package tracking reports.
  • A package that a shipper's agent drops at the wrong USPS facility is mis-shipped, a scan event in package tracking.
  • Loop mail is mail sent to the wrong destination because its barcode or ZIP Code does not match the address. If the barcode or ZIP Code stays uncorrected, automated processing keeps sending it to the same wrong destination, handling it again and again. Machine failures, such as double-feeds or misread addresses, cause loop mail too.
  • In package tracking, event LX, Loop Mail Exception, shows customers a Processing Exception: the local facility is taking steps to correct a processing problem. USPS is retiring LX in PTR2, the platform that runs beside Product Tracking and Reporting until customers migrate to it.
  • Processing exception events flag a package moving from or toward a place hit by a delay, such as missing air or surface transport. Weather, such as a major snowstorm, raises the same kind of event.
  • Inside USPS, an operation's critical entry time is the latest time committed mail can reach it and still meet its service standard. The rest, noncommitted mail, is curtailed when it cannot be cased or processed before the route leaves or the truck departs. USPS calls this delay of mail, and a carrier may leave such mail for casing the next day.
  • Certified Mail moves as ordinary mail in transit, so the service does not speed it up.

Scan events for misrouted packages and processing delays.

PTR Domestic Scan Events, October 2026
EventUSPS.com wordingStatus categoryWhat it means
08Processing at USPS FacilityIn TransitUSPS redirected the item to the correct delivery unit on the next mail dispatch after it was routed incorrectly.
15Processing at USPS FacilityIn TransitA shipping partner or their agent responsible for transporting the item to USPS dropped it at the wrong USPS facility
LXProcessing ExceptionAlertUSPS has detected a processing irregularity for the item.
OXProcessing Exception, Other DelayAlertThe item was either being processed from or headed to a location that is being impacted by a delay of some sort.
TXProcessing Exception, Regional Transportation DelayAlertThe item was either being processed from or headed to a location that is being impacted by a transportation delay (e.g., air or surface transport not available)
WXProcessing Exception, Regional Weather DelayAlertThe item was either being processed from or headed to a location that is being impacted by a weather delay (e.g., major snow storm).

6 codes in the PTR Domestic Scan Events, October 2026, where Event is 08 or 15 or TX or WX or OX or LX.

Index: 28 entries

Systems (11)

Document (1)

Facilities (7)

Terms (9)

Sources