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Traditional ACS

Traditional ACS is the original form of Address Change Service, which sends mailers electronic notices of undeliverable mail and changes of address. A mailer prints a USPS-assigned Participant ID and an optional keyline in the address block and needs no Intelligent Mail barcode. The notices arrive, for a fee, on USPS's Electronic Product Fulfillment website.

Updated October 31, 202640 sources

What it is

Traditional ACS was built for Periodicals mailers and later opened to all mail classes. Mailers of letters, flats and parcels in any class use it to receive electronic address corrections. It dates back to the 1980s.

It is a fee-based Move Update option. Each notice is charged the electronic address correction fee that the Domestic Mail Manual lists. Parcel Select mailers also pay an additional service fee for parcels that are forwarded or returned.

OneCode ACS and Full-Service ACS identify the mailer by a Mailer ID in the barcode. Traditional ACS identifies the mailer by a Participant ID instead, which USPS assigns for one mail class.

Shipper Paid Forwarding is a special subset of Traditional ACS. It lets parcel mailers pay forwarding postage through their ACS account. USPS encourages ACS participants to sign up for SingleSource ACS fulfillment. SingleSource ACS combines the notices of every ACS type into one file format.

How it works

USPS can report a move only when the customer files a change-of-address order. When USPS knows a customer moved without filing, it creates an order itself, such as Moved, Left No Address. These reach the mailer as change-of-address notices with a Do Not Forward code, K or G.

When PARS equipment or a carrier finds a piece undeliverable because the addressee moved, these steps follow.

  1. The piece goes to PARS equipment or the Computerized Forwarding System, depending on class, size and endorsement.
  2. USPS uses the 11-digit delivery point ZIP Code in the barcode to look for an order from that address.
  3. USPS tries to match the name and address to a change-of-address order.
  4. A match on a piece with a readable, valid Participant ID, and keyline where required, produces a notice.
  5. The mail class, the ancillary service and the order's age decide whether the piece is forwarded, discarded or returned.
  6. The notices go to the National Customer Support Center, which sorts them by Participant ID and posts them for download.

Traditional ACS also reports pieces that are undeliverable for reasons other than a move. These reports are nixie notices. A mailer gets nixie notices only when its pieces carry a keyline.

Notices cover the United States and its territories. They also cover moves from a domestic address to a foreign one.

The mailpiece

A Traditional ACS piece carries these lines besides the delivery and return addresses:

  • An ancillary service endorsement, which tells USPS how to handle the piece if it is undeliverable.
  • The Participant ID, after a pound sign, which identifies the sender.
  • The keyline, between pound signs, which identifies the recipient in the sender's mailing list.
  • An optional Intelligent Mail barcode, which can carry a Service Type Identifier, a Mailer ID, a serial number and routing.

The Participant ID, keyline and endorsement are printed in a non-narrow Helvetica or Arial font of at least 8 points. USPS strongly suggests 10 to 12 points.

In a window envelope, the contents must not slip and hide the Participant ID or keyline. USPS strongly recommends a tap test on all sides, including the top, to check for shifting.

The Participant ID

A Participant ID is a code of seven letters, starting with B, that USPS assigns for one class of mail. Only the ACS Department can provide one. It is printed in uppercase on the mailpiece or the first line of the address block, aligned left, after a single pound sign. An example is #BWNBBCD.

The second letter names the mail class, and the ID may be used only on that class:

  • #BW: First-Class Mail
  • #BX: Periodicals
  • #BY: USPS Marketing Mail
  • #BZ: Bound Printed Matter or Package Services

The Participant ID can go on the optional endorsement line, followed by at least one space before anything else on that line. It may also be preprinted on the envelope, on the address label or within the window. The pound sign and Participant ID should not appear on mailings that do not request ACS.

The Participant ID identifies the mailer, the mail class and the ancillary service requested. The ACS Department keeps that information in a mailer profile for each Participant ID.

The keyline

A keyline is a code the mailer creates to identify its own customer, and USPS sets only the rules for making it. It is optional for change-of-address notices but required for nixie notices. It can hold an account number or another identifier for the customer.

A keyline has 4 to 16 characters, including a check digit at the end. It is printed between pound signs, with a space after every fourth character, as in #9876 5432 1#. The pound signs and spaces do not count toward the 16 characters and do not come back in a notice.

Each keyline is numeric, alpha or alphanumeric, and all keylines under one Participant ID must share one length, attribute and check digit algorithm. Numeric keylines hold only digits and cannot be all zeros. Alpha keylines hold the letters A to Z and may use the forward slash, which counts as a letter. Alphanumeric keylines need at least one digit and one letter.

Every keyline ends with a check digit from one of the USPS algorithms, MOD 10, MOD 10 Reverse or MOD 21. MOD 10 Reverse is MOD 10 computed from right to left. USPS calls MOD 21 the strongest, since it prevents typing and transposition errors. MOD 21 ends in a letter, so QWERTY becomes #QWER TYS#.

MOD 10 treats the keyline without its check digit as a string of 3 to 15 characters.

  1. Remove any spaces, then turn each letter into a number by keeping its lower four bits.
  2. Multiply the value at each odd-numbered position by 2.
  3. Add up the digits of each position's value, not the values themselves.
  4. Subtract the right-most digit of the sum from 10 to get the check digit.

A right-most digit of 0 gives a check digit of 0. For the keyline JLSTMS6796, the complete keyline is # JLST MS67 969#.

Endorsements and the profile

Every Traditional ACS piece needs a printed ancillary service endorsement. The mailer also records its chosen ancillary service in a mailer profile that the ACS Department keeps.

Three things can name the service: the printed endorsement, the barcode's Service Type Identifier and the Participant ID's profile. When a barcode is used, its Service Type Identifier takes precedence over the profile. When the printed endorsement conflicts with either, the printed endorsement wins.

Electronic Service Requested is a generic endorsement that stands in for Address, Change or Return Service Requested. Printing it asks USPS to rely on the Participant ID's profile. That lets a mailer use one envelope stock across classes and change the service in the profile. It may be printed only on mail that requests ACS.

Each endorsement comes in options, and the option is recorded in the Service Type Identifier rather than printed. Under First-Class Mail's Change Service Requested Option 1, a forwardable piece is discarded and a notice is generated for the order's 18 months. Under Option 2, the piece is forwarded with a notice in months 1 through 12, then discarded with a notice in months 13 through 18.

Periodicals need no endorsement. A publisher prints Address Service Requested only to have undeliverable copies returned, and then pays the return postage.

Service Type Identifiers

A barcode on a Traditional ACS piece must carry a Service Type Identifier assigned to Traditional ACS. That holds even when the barcode is there only for postage discounts. The mailer should also give the barcode's Mailer ID on its ACS enrollment form.

The Service Type Identifiers that request Traditional ACS, by mail class, endorsement option and service level.

Service Type IDentifier (STID) Table, effective January 21, 2024
STIDMail classOptionService levelInformed Visibility Mail Tracking & Reporting
501First-Class Mail®Address Service Requested Opt 1**Basic or NonautomationWithout IV® MTR
500First-Class Mail®Address Service Requested Opt 1**Basic or NonautomationWith IV® MTR
505First-Class Mail®Address Service Requested Opt 1**Full-ServiceWithout IV® MTR
503First-Class Mail®Address Service Requested Opt 1**Full-ServiceWith IV® MTR
507First-Class Mail®Address Service Requested Opt 2**Basic or NonautomationWithout IV® MTR
506First-Class Mail®Address Service Requested Opt 2**Basic or NonautomationWith IV® MTR
509First-Class Mail®Address Service Requested Opt 2**Full-ServiceWithout IV® MTR
508First-Class Mail®Address Service Requested Opt 2**Full-ServiceWith IV® MTR
517First-Class Mail®Change Service Requested Opt 1** ♻Basic or NonautomationWithout IV® MTR
515First-Class Mail®Change Service Requested Opt 1** ♻Basic or NonautomationWith IV® MTR

1 to 10 of 71 codes in the Service Type IDentifier (STID) Table, effective January 21, 2024, where Group is Traditional ACS™.

Periodicals

Periodicals matched to a change-of-address order are forwarded for 60 days after the move takes effect. The publisher picks a follow-up option that sets how often notices come. Options 1 and 3 do not exist.

  • Option 2: no notice during the 60-day forwarding, then a notice for the first piece after it.
  • Option 4: an immediate notice for the first piece, and no more after that.
  • Option 5: an immediate notice for the first piece, and another for a piece sent after the 60 days.
  • Option 6: an immediate notice for the first piece, none from day 61 to day 120, and one after that.

Options 5 and 6 can produce two identical notices for one customer on the same day. A Periodicals piece that is undeliverable for another reason brings a nixie notice and is discarded.

Fulfillment files

USPS posts fulfillment files to the Electronic Product Fulfillment website daily. Each file is a ZIP archive protected with an 18-character password. It holds an ACS notice file with the notices and a shipping notice file with record counts. The notice file uses the ACS 702-character fixed format, with optional CSV and Excel versions. The website deletes notification files older than 95 days.

Software that reads the files must check each record and field against the file layouts. The ACS File Format Technical Guide gives the layouts.

The ACS billing cycle runs from the 25th of one month to the 24th of the next. Payment is due with the remittance slip within 30 days of the invoice date. Balances unpaid after 30 days are charged 10 percent annual interest. Accounts with an SS prefix get electronic invoices on their fulfillment account when the balance is over $25.

Enrollment

A mailer enrolls in ACS to be assigned a Participant ID by the ACS Department at the National Customer Support Center in Memphis. It also submits PS Form 5116 to get access to the Electronic Product Fulfillment website. Each customer must give a dedicated email address for ACS communications. A sample process then checks the mailpiece before production.

  1. Create sample pieces with the Participant ID, the optional keyline and customer information in the address block.
  2. If the pieces carry a barcode, include a Traditional ACS Service Type Identifier, the Mailer ID and a serial number.
  3. Give every piece a valid domestic return address on the address side.
  4. Mail at least 20 finished sample pieces to the ACS Department in Memphis.
  5. Wait for the ACS Department to report that the samples are approved.
  6. Check the piece against the ACS Department's documentation, then begin production.

Rules

To use Traditional ACS, you must add the ACS Participant ID (also known as the Participant Code) assigned by the Postal Service™ to the address block of your mailpiece.

A mailer must put the Participant ID that USPS assigned into the address block of each piece.

To meet the Move Update Standard, mailers must use the Traditional ACS notices received to update the address within 95 days of the Move Effective Date.

A mailer must update each address from its notices within 95 days of the move's effective date to meet the Move Update standard.

If the Intelligent Mail barcode is used, the Service Type ID used in the Intelligent Mail barcode must be specifically assigned for use with Traditional ACS.

A barcode on the piece must carry a Service Type Identifier assigned to Traditional ACS.

All mail that is prepared for Traditional ACS requires a printed ancillary service endorsement.

Every Traditional ACS piece must carry a printed ancillary service endorsement.

All Traditional ACS mailpieces, as with all mail requesting ancillary services, must have a domestic Return Address properly appearing on the front of the mailpiece.

Every piece must show a domestic return address on its front.

The Participant ID for a specified class of mail must be placed on the correct class of mail.

A Participant ID must go only on the mail class it was assigned for.

It is required that all keylines end with an approved Postal Service™ check digit, which may be numeric or alpha, depending on the check digit algorithm selected.

Every keyline must end with a check digit USPS approves, which may be a number or a letter depending on the algorithm.

Before making any modifications to your NCSC-preapproved keyline characteristics (length, attribute or check digit algorithm), you must notify the ACS Department at the NCSC.

A mailer must tell the ACS Department before changing a keyline's length, attribute or check digit algorithm.

What goes wrong

ACS is not a guaranteed service, and manual notices may still arrive, though fewer of them.

USPS lists these as the most common mistakes on a Traditional ACS piece:

  • No return address on the address side.
  • A missing or invalid printed endorsement, or one whose size, read direction or clearance fails the Domestic Mail Manual.
  • A Participant ID printed wrongly, in its font size, its location or its # delimiter.
  • A missing or malformed keyline: its length, makeup, check digit or # delimiters.
  • A Service Type Identifier in the barcode that does not request Traditional ACS.
  • Traditional ACS information hidden or crowded in a window envelope.
  • An exceptional address format such as Or Current Resident.

A specific printed endorsement can bring hardcopy notices or returned mail when the Participant ID or a required keyline cannot be read. A piece with both a barcode and a Participant ID still yields a Traditional ACS notice, at the electronic fee, when the barcode cannot be read.

The ACS Department needs notice at least 7 days before mailing when a mailer changes any of these on an approved piece:

  • The printed ancillary service endorsement.
  • The location or configuration of the Participant ID.
  • The configuration, attributes or check digit computation of the keyline.
  • The Service Type Identifier in the barcode.
  • The Mailer ID in the barcode.

Changing keyline characteristics without notice could end all electronic corrections and leave only manual ones.

USPS does not process change-of-address orders from single-point deliveries such as colleges, prisons and hospitals. Pieces those institutions return produce no ACS records. A notice's name may not match the name on the original piece. USPS strongly suggests not relying on the keyline alone when updating files.

Mailing to an addressee more than 95 days after the move's effective date risks Move Update error assessment charges.

Delinquent accounts may see ACS fulfillment interrupted and get manual notices or returned mail instead. Requests to refund wrongly charged records go to acs@usps.gov within 45 days of receiving the invoice. USPS gives no refund when pieces were prepared wrongly or a requested service was provided.

Terms

Address Change ServiceACS, Address Correction Service
a post-mailing service that provides USPS with instructions on how to handle Undeliverable as Addressed (UAA) mail and provides you with electronic Change of Address (COA) information or the reason for non-delivery
Participant IDPID, ACS Participant ID, Participant Code, ACS participant code, traditional ACS Participant ID/Code
The Participant ID is always a 7-character alpha string that is preceded by a pound sign symbol, for example, #BWNBBCD.
Keylinetraditional ACS Keyline
a unique code generated by the mailer that may incorporate customer identifiers
Nixie NoticeNIX, Nixie notifications, ACS Nixie Notices
information on addresses that are undeliverable for reasons other than a customer move
Ancillary Service EndorsementASE
a post-mailing, on-piece printed endorsement used to instruct the Postal Service regarding the appropriate disposition, upon determining that it is Undeliverable-asAddressed (UAA): Address Service Requested, Change Service Requested, Return Service Requested.
Electronic Service RequestedESR
a generic endorsement that instructs Post Offices to send UAA mail to a CFS or PARS operation so an electronic ACS notice can be generated
Service Type IdentifiersSTID, STIDS, STI, Service Type IDs, Service Type ID(s)
A unique three-digit code embedded in the Intelligent Mail® barcode (IMb®) that indicates the service type for an individual mailpiece.
Electronic Product FulfillmentEPF, Electronic Product Fulfillment (EPF) web site, Electronic Fulfillment Website
A secure web-based application managed by the National Customer Support Center in Memphis TN that is used to post and receive Address Management and Address Information System products, including ACS fulfillment files.
Optional Endorsement LineOEL
A series of specific printed characters on the top line of the address block that identifies the sortation level of a bundle and may contain an ACS participant code.
Undeliverable as AddressedUAA, UAA mail
mail that the USPS cannot deliver as addressed and must be forwarded to the addressee, returned to the sender, or discarded depending on the authorized treatment for that mail class and/or specific instructions provided by the mailer through ancillary service requests
Change-of-AddressCOA, change-of-address order, changes-of-address
When a customer moves from one mailing address to another and wants the Postal Service to forward their mail, they notify the post office of the permanent or temporary change-of-address (COA).
Shipper Paid ForwardingSPF, Shipper Paid Forwarding option
is an ACS fulfillment option that allows parcel mailers to receive and electronic address correction and pay forwarding postage via their ACS account

Documents

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Publications

User Guides

FAQs

Announcements

Data Files

Tools

Applications/Forms

Contacts

The ACS Department at the National Customer Support Center answers questions at acs@usps.gov or (877) 640-0724, option 1. Its mailing address is ACS Dept, National Customer Support Center, 225 N Humphreys Blvd Ste 501, Memphis TN 38188-1009. The NCSC Accounts Receivable Department answers credit card and ACH payment questions at 901-681-4658. Mailpiece Design Analysts help with mailpiece design at mda@usps.gov.

Sources