Postal Dictionary
Your Postal Dictionary of Commonly Used Terms, Acronyms, and Abbreviations
Cornerstone Services, Inc. has compiled a postal dictionary featuring commonly used terms in direct mail marketing. The Post Office often uses "insider" terms that remain undefined for the general public. Most people recognize basic acronyms such as PO Box, ZIP Code, or First-Class Mail. However, if you are new to direct mail or frequently interact with the Post Office, this dictionary will provide essential information to help you navigate mailing processes.
Terms and Definitions Within Our Postal Dictionary
ADC (Area Distribution Center)
ADC refers to a group destination for mail pieces that undergo presort bundling and trying before reaching a regional service area facility. For example, a presorted bundle of letters heading to the NEW YORK, NY 100 ADC would contain mail with ZIP Codes beginning with "100," "101," "102," or "104." Similarly, a bundle directed to PHILADELPHIA, PA 190 ADC would only include ZIP Codes starting with "190," "191," or "192." Upon reaching the ADC destination, USPS personnel separate the mail into specific 5-Digit ZIP Codes for carrier route distribution.
AADC (Automated Area Distribution Center)
An AADC operates similarly to an ADC (see definition above in this postal dictionary). However, it features specialized automation-handling systems that process automation-prepared mail, including letters, flats, and parcels. On a postage statement, “Mixed AADC” or “Mixed ADC” indicates that the addressed materials in a tray, sack, or bundle are sorted for multiple AADC or ADC facilities rather than a single destination.
APO (Army Post Office™)
APO addresses appear in large mailing databases or Board of Election files. Typically, these recipients are younger military service members. APOs fall under the jurisdiction of Postmasters in New York or San Francisco. However, MPOs (Military Post Offices) serve overseas US military bases across all branches, including the Army, Navy, Air Force, and Marines.
BMEU (Business Mail Entry Unit)
A BMEU is a USPS facility where discounted First-Class and Marketing (Bulk) Mail enters the system. The United States has approximately 2,500 BMEUs, though they are not always conveniently located. You can find a nearby BMEU using the USPS® locator. Unlike EDDM® discounted mail, all other USPS® discounted mail must be entered through a BMEU window.
BPM (Bound Printed Matter)
BPM applies to catalogs, books, and directories weighing between 1 lb. and 15 lbs. These materials must have permanently bound sheets and contain at least 90% advertising, promotional, or informational content. While phone books were once mailed at BPM rates, businesses now primarily use BPM for product guides in industries like automotive parts, plumbing supplies, and theatrical rigging.
BRM (Business Reply Mail®)
BRM allows recipients to return mail without paying postage. Instead, the sender or business assumes the postage cost upon receipt.
Bundles
Bundles refer to grouped mail prepared for discounted mailing rates. This applies to both Letters and Flats. The preparation process differs between Flat-rate and Letter-rate bundles. If you are reading this postal dictionary, you are likely not a commercial mailer. In that case, you may prepare a letter-rate mailing as a non-barcoded but addressed presort mailing. It may also qualify as a DMM mailing or a saturation Simplified Address mailing.
CASS™ (Coding Accuracy Support System)
CASS Certification ensures an address has been "ZIP+4 verified" and recognized by the US Postal Service® for accuracy.
CR / CRRT (Carrier Route)
Carrier Routes classify mail into different categories such as Rural (Carrier) Routes and City (Carrier) Routes. USPS assigns additional carrier routes as ZIP Codes expand. Discounted postage rates apply when a mailing reaches a specific percentage of households or businesses within a Carrier Route.
For instance, ECRWSS (Enhanced Carrier Route Walking Sequence Saturation) ensures that every address within a carrier route receives a mail piece, making it the most cost-effective bulk mailing option. Here’s the Postal Explorer link for more info about Carrier Route mailings.
CRM (Courtesy Reply Mail)
A CRM envelope requires the recipient to affix a stamp before mailing it back. These envelopes, also known as Courtesy Reply Envelopes (CREs), often come in #9, #6 3/4, and A2 sizes. Unlike BRM, where the sender covers the postage, CRM requires the recipient to pay.
DDU (Destination Delivery Unit)
Similar to ADC or AADC (see their definitions above), DDU refers to a pricing classification for mail. This applies to flats or parcels but no longer includes letters. Mailers enter these at the "destination delivery unit" (DDU) for local ZIP Code delivery.
USPS offers a "DDU discount" as an incentive for handling part of the delivery process. By delivering mail directly to the local 5-digit ZIP Code post office, mailers reduce USPS sorting work. In return, USPS grants a larger postage discount compared to other rate tiers.
Not all post offices accept DDU entry discounts. Calling ahead ensures that the post office will process the mailing without issues.
DMM® (Domestic Mail Manual)
The DMM outlines all mailing standards and prices set by the United States Postal Service®. USPS no longer prints the manual, but you can access it online through this link. Additionally, Postal Explorer provides a direct link to the DMM along with other valuable postal references.
DPV® (Delivery Point Validation)
You might recognize ZIP+4, but DPV goes a step further. ZIP+4 verifies that an address exists, while DPV ensures that mail can be successfully delivered to that address. If you want more details, here’s a helpful overview.
ECRWSS (Enhanced Carrier Route Walk Sequence)
ECRWSS describes a discounted postage rate class for mail targeting a specific carrier route. Your mailing must cover at least 90% of all residential addresses on the route or at least 75% of both business and residential addresses. Mailpieces, whether letters or flats, must be arranged in house-by-house order. This allows the postal carrier to deliver them sequentially while walking the route.
EDDM® (Every Door Direct Mail™)
The USPS® introduced the EDDM® program to help customers send qualifying Flat-rate mail using Simplified Addressing. For example, mailpieces can be addressed as “Local Postal Customer” to reach specific carrier routes within a designated post office. As of 2018, realtors and small businesses have been the primary users of this program, particularly those targeting customers near a physical storefront.
However, non-profits rarely use EDDM® since it is not an ideal tool for fundraising or securing discounted postage. For more USPS® intel, including EDDM® sizes, prices, and mapping tools, click on the link.
FCM (First-Class Mail®)
The most important aspect of First-Class Mail is its higher internal delivery standards compared to lower-tier mail classes such as Marketing Mail, Parcel Mail, and Non-Profit Org qualifying mail. Except for Priority Express Mail, First-Class Mail remains the fastest USPS® delivery classification. Both First-Class Mail and Priority Mail follow internal delivery standards ranging from one to three days.
FIM (Facing Identification Mark)
The USPS® uses five types of Facing Identification Marks (FIMs), but the most common is FIM A, which appears on Courtesy Reply Envelopes. This FIM consists of five vertical lines (technically a binary code) positioned at the top-right center of an envelope or return postcard. It signals to the USPS® that the mail piece is automation-compatible and that the sender, not the recipient, will cover the postage, typically with a stamp.
Additionally, USPS® requires that if you claim automation discounts for the outer mail piece, any enclosed items must also meet automation handling standards.
The second most common FIM is FIM C, which is essential for Business Reply Mail (BRM). This mark notifies the destination post office that these return cards require special handling and that the recipient, rather than the sender, will pay the postage and any additional fees.
Flat
The Postal Service® defines "flats" as large envelopes, newsletters, and magazines. For a mailpiece to qualify as a flat, it must meet at least one of the following criteria:
- Height: Taller than 6 1/8 inches
- Length: Longer than 11 1/2 inches
- Thickness: More than 1/4 inch
If a mailpiece meets any of these size requirements, it falls under the flats category. You can view current flats postage rates here.
HCR (Highway Contract Route)
Highway Contract Routes (HCRs) function similarly to Rural Routes (RRs) but operate under postal contractor agreements rather than USPS-employed carriers. These routes primarily serve rural areas, ensuring mail transportation along designated highway routes between specific points.
Previously known as “Star Routes,” this outdated term is no longer in use. However, the core function of HCRs remains the same—providing efficient mail delivery in areas where USPS does not employ full-time carriers.
IMb™ (Intelligent Mail® barcode)
The Intelligent Mail® barcode (IMb™) replaces the Delivery Point Barcode (DP), often called the "picket fence" barcode due to its visual appearance. Unlike its predecessor, the IMb™ consolidates multiple data points into a single, self-contained barcode, enhancing tracking and automation capabilities.
This barcode encodes essential information, including:
- The Mailer ID assigned by USPS®
- The mail class (e.g., First-Class Mail or Bulk Mail)
- A unique serial number for the mail piece
- The destination routing code for accurate processing
For further details on IMb™ specifications and benefits, visit this link.
IMM® (International Mail Manual)
Most people refer to the International Mail Manual (IMM®) for proper formatting of foreign country names when addressing international mail. Additionally, the IMM® provides important guidelines on mailing restrictions, including prohibited and restricted items for each destination country. For more details, consult the IMM® to ensure compliance with international mailing regulations.
IMpb (Intelligent Mail® package barcode)
(a) The USPS® requires Intelligent Mail® package barcodes (IMpb™) on all parcels, ensuring complete tracking visibility within its system. (b) Additionally, IMpb™ provides advanced data quality feedback to the USPS®, which may result in penalties if a mailer fails to meet automation quality thresholds.
Indicia (postal permit mark or box)
For large-volume mail, we typically place a pre-printed postal permit box at the upper right-hand corner of an envelope, flat, or similar mailpiece. This box indicates (a) the class of mail and (b) that postage has been prepaid for the mailing.
Alternatively, instead of using an indicia, you may apply First-Class Mail stamps, pre-canceled stamps, or a meter mark. When designing a mail piece, you must ensure the indicia aligns at a right angle to the address block, whether it contains a Simplified Address or a standard recipient address.
Letter
The "Letters" class of mail includes mailpieces that measure between 3 1/2″ and 6 1/8″ in height, 5″ and 11 1/2″ in length, and 0.007″ to 1/8″ in thickness.
Examples of Letter-rate mail include #10, #9, and #6 3/4 business envelopes, as well as A-size envelopes such as A8, A7, A6, and A2.
NCOA™ (National Change of Address)
The NCOA™ (National Change of Address) service connects with the USPS® NCOALink database, which contains approximately 160 million change-of-address records. It provides details on the movement of individuals and businesses across the United States and its territories for those who have officially requested address updates.
The NCOALink database undergoes constant updates to maintain accuracy. However, many consumers mistakenly believe that USPS® tracks every address change, when in reality, the system only records updates submitted through the National Change of Address program.
NDC Presort price (Network Distribution Center Presort price)
The NDC Presort Price (Network Distribution Center Presort Price) offers a unique presort discount rate for mailers who submit their mailings directly to a USPS® Network Distribution Center (NDC).
Your nearest postal center might be an NDC, though there are currently only 22 NDCs across the United States, primarily located in metropolitan areas. You can find the complete list of NDCs here.
PAVE™ (Presort Accuracy Validation and Evaluation)
The PAVE™ (Presort Accuracy Validation and Evaluation) program is a USPS® process designed to assess mailing software quality in collaboration with the private sector.
To achieve PAVE certification, software developers and providers must demonstrate that their address handling technology meets USPS® accuracy standards and ensures proper mail processing.
PCSC (Pricing and Classification Service Center)
The PCSC (Pricing and Classification Service Center), located in New York City, serves as the USPS® decision bureau responsible for evaluating and ruling on various domestic and international mailing classifications.
Additionally, the PCSC oversees pricing decisions and grants privileges such as non-profit mailing eligibility and periodical mailing authorization.
PO Box (Post Office™ Box)
Two important things to understand about PO Boxes:
First, PO Boxes differ from generic "Boxes." If you do not include “PO Box” along with a number (and sometimes a legacy letter), "Box" may not refer to a Post Office Box. Instead, it could indicate a private mailbox, which is an important distinction.
Second, some towns—either partially or entirely—require PO Boxes instead of delivering mail to street addresses. In these cases, using a street address may not guarantee delivery. To ensure reliable mail receipt, always use a PO Box whenever applicable.
Presort
Presort refers to the process where a mailer organizes mail to meet the finest level of sorting required for the postage rate being claimed.
Typically, presorting follows a sequential process, starting from the lowest (most detailed) level and progressing to higher levels. Mail pieces are grouped according to specific USPS destination standards, ensuring efficient handling.
However, not all presort levels apply to every mailing situation, as different classifications have unique sorting requirements.
PRSRT STD (Presorted Standard Mail)
PRSRT STD (Presorted Standard Mail) is another term for Bulk Mail. Over the years, it has also been referred to as Third Class Mail, Advertising Mail, Standard Mail, and Standard "A" Mail.
Since 2017, USPS has officially renamed it Marketing Mail. This classification offers discounted postage rates for bulk mailings, including non-profit (not-for-profit) mail, making it a cost-effective choice for mass mailing campaigns. Click here for more information.
PS (Postage Statement)
A postage statement is a required form that mailers complete when submitting mailpieces—such as letters, parcels, or flats—at discounted postage rates.
All USPS® postage statements begin with “PS Form”, and you can find the complete list at the USPS® website.
If you plan to conduct a regular bulk mailing and possess the necessary mailing permits, you will most likely need to use PS Form 3602-R.
RR (Rural Route)
Rural Routes (RRs) are essential for preparing mail destined for post offices that provide rural route delivery. Even in areas like Westchester County, NY—which is largely metropolitan—Rural Routes exist, particularly in the northern part of the county.
If you are planning a saturation mailing to a ZIP Code with rural routes, you must identify both the RR number and the number of deliverable addresses on that route. You can use this link to obtain the necessary address counts if you are preparing your own mail.
In some cases, you may encounter addresses formatted as "RR [#] BOX [###]". However, many states have phased out this type of rural addressing since emergency services—such as ambulances and fire trucks—require more precise locations to ensure efficient response times.
RTS (Return-To-Sender)
Postal carriers often write "RTS" (Return to Sender) on returned First-Class Mail. While they are supposed to indicate the reason for the return, this information is often missing or illegible.
Some of the most common RTS reasons include:
- NFA (No Forwarding Address) – The recipient moved but did not leave a forwarding address.
- NSA (No Such Address) – The address does not exist or contains errors.
- NMR (No Mail Receptacle) – There is no mailbox at the address.
- Refused – The recipient explicitly declined to accept the mail.
- Deceased – The intended recipient has passed away.
SCF (Sectional Center Facility)
A Sectional Center Facility (SCF) serves as both a major mail entry and a mail processing hub within the USPS® network. Typically, an SCF has an on-site Business Mail Entry Unit (BMEU) window, where bulk mailings enter the system.
The United States has approximately 350 SCFs, each responsible for distributing mail to multiple ZIP Codes. SCFs oversee regional mail distribution, functioning as collection points for 5-digit ZIP Code post offices.
For discounted mail, SCFs play a crucial role. Mail entered at an SCF receives better postage rates than mail entered at a Network Distribution Center (NDC) but does not qualify for the deeper discounts of Destination Delivery Unit (DDU) entry.
Businesses can achieve significant postage savings by presenting their mail at an SCF rather than a more convenient but higher-cost BMEU window. However, it's important to note that state lines do not always determine SCF service areas, and changes in SCF assignments can occur over time.
For a current list of SCFs, refer to this official USPS resource.
Simplified Address
Simplified Addresses typically appear as “Postal Customer,” “Postal Patron,” “Current Resident,” or “Current Boxholder.” Unlike traditional addresses, these labels do not include specific street names or house numbers, which can sometimes cause confusion.
This form of addressing primarily serves saturation mailing purposes, ensuring that every household or business within a selected PO Box area or carrier route receives the mailpiece. Businesses and organizations use Simplified Addresses when sending bulk mail to maximize reach without needing a precise mailing list.
ZIP Code™ (Zone Improvement Plan Code)
In 1963, the USPS® introduced the ZIP Code™ system as a mandatory requirement for domestically addressed mail. The increasing mail volume made it impractical to sort mail without a standardized numeric system. By implementing ZIP Codes, the USPS® significantly improved sorting efficiency and delivery speed.
3-Digit
3-Digit refers to the first three numbers in a 5-Digit ZIP Code. Mailers commonly use this term in 3-digit presort preparation for bundling letters and flats. Additionally, it plays a crucial role in setting up ADC or AADC destination trays or sacks, ensuring efficient mail processing for both letters and flats.
5-Digit
All ZIP Codes contain five digits, but mailers typically use the term 5-Digit in the context of presorted mail preparation. This process closely resembles 3-Digit bundle or tray preparation, where mail is sorted for efficient delivery.
Our postal dictionary undergoes regular updates to include newer and increasingly popular mailing terms, ensuring the most up-to-date information for users.
If there is a term, acronym or abbreviation you don’t see on our postal dictionary page then check out the USPS postal terms page.