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Intelligent Mail Package Barcode (IMpb) ACS

IMpb ACS is a USPS service that gives parcel mailers who print the Intelligent Mail package barcode an electronic address correction. A shipper registers its Mailer ID, and a printed ancillary service endorsement on the parcel then triggers an electronic notice.

Updated October 28, 202633 sources

What it is

IMpb ACS is one of the ways to take part in Address Change Service, which replaces manual address correction notices with electronic ones. The other ways include OneCode ACS and Traditional ACS.

IMpb ACS reads the Intelligent Mail package barcode, and taking part requires that barcode. The Mailer ID, a six- or nine-digit number in the barcode, decides which shipper receives each notice.

USPS supports ACS through the National Customer Support Center in Memphis TN. Its ACS Department keeps each shipper's ACS profile.

A notice reports a change-of-address order the addressee filed. It can also report a parcel that is undeliverable for a reason other than a move.

IMpb ACS is available for these parcels:

  • USPS Ground Advantage and Priority Mail parcels
  • Periodicals mailed as parcels
  • Parcel Select
  • Package Services, including Library Mail and Media Mail
  • USPS Marketing Mail parcels
  • Bound Printed Matter, including Bound Printed Matter flats

How it works

The same steps follow for every undeliverable parcel, whatever the reason. When the addressee has moved without telling USPS, the delivery employee files the move as Moved, Left No Address or Box Closed No Order. A parcel undeliverable for another reason produces a Nixie notice, which gives only the reason.

What happens to an undeliverable parcel with IMpb ACS.

  1. The Remote Forwarding System or the Computerized Forwarding System processes the parcel.
  2. The system tries to match the name and address to a change-of-address order.
  3. A match makes an ACS change-of-address notice, and no match makes a Nixie notice.
  4. The mail class, the endorsement's service and the order's age decide what happens to the parcel.
  5. USPS applies a forwarding, return or waste label to the parcel.
  6. The National Customer Support Center sorts each notice by the Mailer ID in the barcode.
  7. USPS fulfills the notices daily through Electronic Product Fulfillment.
  8. Tracking reports a Forwarding Processed or Return Processed event for the parcel.

The PTR event for a processed forward.

PTR Domestic Scan Events, October 2026, 06-37

Extract description
FORWARD PROCESSED
USPS.com wording
Forward Processed
Status category
Alert
What it means
USPS took action to ensure that the forwarding instructions have been applied to the package.
Starts the clock
No
Stops the clock
Yes

The PTR event for a processed return.

PTR Domestic Scan Events, October 2026, 29-37

Extract description
RETURN TO SENDER PROCESSED
USPS.com wording
Return to Sender Processed
Status category
Alert
What it means
USPS has processed the return based on the package characteristics.
Starts the clock
No
Stops the clock
Yes

The Mailer ID

The Mailer ID in the barcode routes every notice to the shipper that registered it. It also picks the shipper's endorsement option.

An illustrative Priority Mail barcode with a nine-digit Mailer ID.

9205590190190100000018

The Mailer ID and serial number are examples.

    A Mailer ID registered for IMpb ACS also gets Option 1 service on parcels of other mail classes with an ACS-capable endorsement.

    A service provider may print a different Mailer ID in the barcode from the one in its Shipping Services File.

    Endorsements and options

    Every parcel that asks for IMpb ACS carries a printed ancillary service endorsement. The shipper registers its endorsement option for each Mailer ID in its ACS profile with the ACS Department. The option number itself is never printed on the parcel.

    A shipper can change one parcel's handling by printing a different ACS-capable endorsement on it.

    Electronic Service Requested is a generic endorsement that sends an undeliverable parcel to forwarding processing so a notice can be made. With it, the Mailer ID picks the option, so each endorsement and option needs its own Mailer ID.

    For a USPS Ground Advantage parcel matched to a change-of-address order, each option handles the parcel this way:

    • Change Service Requested Option 1 discards it for the 18-month life of the order and sends the new address.
    • Change Service Requested Option 2 forwards it in months 1 to 12 and discards it in months 13 to 18.
    • Address Service Requested Option 1 forwards it in months 1 to 12, then returns it in months 13 to 18 with no notice.
    • Address Service Requested Option 2 forwards it in months 1 to 12, then returns it in months 13 to 18 with a notice.
    • Return Service Requested Option 2 returns it with the new address for all 18 months, with a notice.

    Shipper Paid Forwarding and Return

    Shipper Paid Forwarding and Return is an IMpb ACS option that lets a shipper pay forwarding or return postage through its ACS account. It is available for these parcels:

    • Parcel Select
    • Package Services, including Library Mail and Media Mail
    • Bound Printed Matter
    • USPS Marketing Mail parcels

    Forwarded Package Services and Bound Printed Matter parcels arrive Postage Due at the new address. If the addressee refuses to pay, the parcel goes back and USPS charges both forwarding and return postage. Shipper Paid Forwarding lets the shipper pay instead, so the addressee is less likely to refuse the parcel.

    Shipper Paid Forwarding and Return needs Shipping Services File version 1.7 or higher. The ancillary service endorsement field of each detail record holds one of two codes:

    • K: Shipper Paid Forwarding, with Change Service Requested Option 2 or Address Service Requested Option 1 or 2.
    • J: Shipper Paid Forwarding and Return, with Address Service Requested Option 3.

    For Shipper Paid Return, each detail record also carries the return address ZIP Code.

    Shipper Paid Forwarding and Return covers only parcels that match the mail class and endorsement registered for the Mailer ID. A shipper who wants it on every parcel registers a different Mailer ID for each mail class and endorsement.

    The ACS notice

    USPS posts the notices daily to Electronic Product Fulfillment, its secure fulfillment website, in zipped, password-protected files. Notification files more than 95 days old are deleted.

    The Deliverability Code field tells what kind of notice a record is:

    • A space marks a forwardable change-of-address order, with the old and new address.
    • W marks a temporary move, with no new address.
    • A USPS-filed action, Moved Left No Address or Box Closed, has a code of K or G and no new address.
    • One of 15 Nixie codes gives the reason a parcel could not be delivered.

    The Mailpiece Identifier field holds the serial number from the barcode. In a Nixie record, the old five-digit ZIP Code field is all zeroes.

    Enrolling

    1. Certify the Mailer IDs for the Intelligent Mail package barcode.
    2. For Shipper Paid Forwarding or Return, confirm Shipping Services File version 1.7 or higher.
    3. Choose the ancillary service, its option and the printed endorsement.
    4. Test printing the barcode's serial number and reading a test fulfillment file.
    5. Complete the ACS Enrollment Form to request IMpb ACS.
    6. Complete PS Form 5116 for access to Electronic Product Fulfillment.
    7. Make copies of the forms and keep one.
    8. Send copies of the forms to the ACS Department by email, fax or mail.
    9. The ACS Department emails the ACS account information within 10 days.

    The ACS Enrollment Form comes with a check list of what it needs, to avoid delays in enrollment:

    • A Federal Taxpayer ID for the billing contact.
    • A company distribution email address in the Communications section.
    • The IMpb ACS box, checked in the ACS Mailer Options section.
    • The Mailer ID the barcode encodes, with one or more mailpiece titles.
    • The endorsement and option code in each mail class column.
    • The Yes box, checked when the Mailer ID uses Shipper Paid Forwarding or Return.
    • A signed and dated authorization statement.

    The Mailer ID and mailpiece titles appear in the daily fulfillment shipping notice sent with the ACS data. The endorsement and option code can be changed later. A shipper that checks SingleSource ACS gets Full Service ACS notices delivered with its other ACS types.

    Fees and billing

    Each change-of-address or Nixie notice costs an Electronic Address Correction Fee on the monthly ACS invoice. The billing cycle runs from the 25th of one month to the 24th of the next. Within 6 days after a cycle ends, USPS posts the invoice to the Electronic Product Fulfillment account as a CSV file and a PDF. Payment is due within 30 days of the invoice date. Balances unpaid after 30 days carry an annual interest rate of 10 percent.

    Parcel Select shippers pay an Additional Service Fee on each forwarded or returned parcel. With Shipper Paid Forwarding and Return, that fee is the reduced ACS Shipper Paid Additional Service Fee on the ACS invoice.

    Rules

    A printed ancillary service endorsement is required for IMpb ACS.

    A parcel must carry a printed ancillary service endorsement to get IMpb ACS.

    Required Mailer IDs (MIDs) must be certified for IMpb prior to enrolling for IMpb ACS.

    A shipper must certify its Mailer IDs for the Intelligent Mail package barcode before it enrolls.

    IMpb ACS and IMpb ACS with SPF/R mailers must register their ancillary service option choice in the mailer profile maintained by the NCSC ACS Department.

    A shipper must register its endorsement option in its ACS profile with the ACS Department.

    Before making any modifications to your printed ancillary service endorsement, you must notify the ACS Department at the NCSC.

    A shipper must tell the ACS Department before it changes the printed endorsement.

    For those parcels that request Shipper Paid services, Shipping Services File version 1.7 or higher is required.

    Shipper Paid parcels must be reported in Shipping Services File version 1.7 or higher.

    “Electronic Service Requested” may be printed only on parcels requesting IMpb ACS or IMpb ACS with SPF/R.

    A shipper may print Electronic Service Requested only on parcels that request IMpb ACS.

    All IMpb ACS parcels must have the domestic return address properly appearing on the address side of the mailpiece.

    Every IMpb ACS parcel must show a domestic return address on its address side.

    The literal "Option” and the associated number must not be printed on the mailpiece.

    A shipper must not print the word Option or its number on the parcel.

    What goes wrong

    A parcel with no printed endorsement gets no IMpb ACS, even with a registered Mailer ID. When the barcode cannot be scanned on a parcel endorsed Electronic Service Requested, USPS treats the parcel as unendorsed. Changing the printed endorsement without telling the ACS Department can end electronic corrections and leave only manual ones.

    Some notices cannot be made, and the parcel is forwarded Postage Due or returned with no notice. ACS is not a guaranteed service, and manual notices can still arrive. Parcels returned by single-point deliveries, such as prisons, hospitals and commercial mail receiving agencies, produce no ACS records.

    A notice's name or old address may not match the original parcel. USPS strongly suggests not relying on the barcode data or serial number alone when updating addresses. A mailer that also leaves Traditional ACS codes on the parcel may get duplicate notices for one change-of-address order.

    Disputed charges go by email to acs@usps.gov with the disputed records. The request must arrive within 45 days of receiving the invoice. No refund is given when a parcel was prepared incorrectly or a requested service was provided. Delinquent accounts can lose ACS fulfillment and get manual notices or returned mail.

    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
    Intelligent Mail Package BarcodeIMpb
    An IMpb is the USPS-developed barcode that can be read by automated parcel-processing equipment and scanning devices and consists of a data string that generally follows the GS1-128 specification.
    Mailer IdentifierMID, Mailer IDs, Mailer Identification, Mailer Identification Number, USPS Mailer ID
    MID is a unique 6- or 9-digit number that identifies the mailer or the mailer’s client.
    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.
    ACS Profilemailer profile
    The ancillary service and the preferred option are recorded in the mailer profile for the Mailer ID that is registered for use for IMpb ACS and is maintained by the NCSC ACS Department.
    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
    Nixie NoticeNIX, Nixie notifications, ACS Nixie Notices
    information on addresses that are undeliverable for reasons other than a customer move
    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
    Shipper Paid ServicesSPS, SHIPPER PAID SERVICES, SPF/R, Shipper Paid Forwarding / Return, Shipper Paid Forwarding / Return (SPF/R) service, SHIPPER PAID FORWARD\RETURN
    an ACS fulfillment option that allows parcel mailers to receive an electronic address correction and pay forwarding or return postage via their ACS account
    Shipping Services FileSSF, Shipping Service Files
    The electronic file containing all manifest and payment information.
    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.

    Documents

    Tech Guides

    Publications

    User Guides

    Contacts

    The ACS Department answers questions at acs@usps.gov or (877) 640-0724.

    Enrollment forms go to the ACS Department by fax at 901-821-6204. They can also go by mail to 225 N HUMPHREYS BLVD STE 501, MEMPHIS TN 38188-1009.

    The National Customer Support Center's Accounts Receivable Department answers questions about card and ACH payments at 901-681-4658.

    Sources