Postal Dictionary


Your postal dictionary of commonly used terms, acronyms and abbreviations.

Cornerstone Services, Inc. has compiled a postal dictionary of the more commonly used definitions you might encounter when using direct mail marketing. The Post Office tends to use a lot of “insider” terms when dealing with mail and generally does not define them for you. Most people have only heard of the generic acronyms or abbreviations such as PO Box, ZIP Code or First Class Mail. If you are getting started with direct mail or frequently interacting with the Post Office, this postal dictionary should provide the essential information you need to mail.

Terms and definitions within our Postal Dictionary

ADC (Area Distribution Center)

Typically used in context of presort bundling and traying; denotes a group destination for mail pieces heading for delivery at a regional service area facility. Examples: a tray tag or presort bundle of letters or flats heading to the NEW YORK, NY 100 ADC would ONLY contain mail pieces starting with first three (3) digits in the 5-Digit ZIP Code : “100”, “101”, “102” or “104”. If the tray or bundle were headed to the PHILADELPHIA PA 190 ADC, then all ZIP Codes in such trays/bundles would ONLY have ZIP Codes that started with “190”, “191” or “192” 3-Digits. Once the tray/bundle reached the ADC destination, it would be broken down to specific 5-Digit ZIP Codes and carrier routes for local distribution.

AADC (Automated Area Distribution Center)

Same as ADC (definition above in this postal dictionary) except that the USPS® destination facility has specific automation-handling equipment for automation prepared ADC mail (letters, flats and/or parcels). On a postage statement, the term “Mixed AADC” or “Mixed ADC” simply means that addressed materials within a tray, sack or bundle are intended for one or more AADC, ADC, etc.

APO (Army Post Office™)

We’ll see “APO” occasionally in large address databases or even Board of Election files. The recipients tend to be younger and are usually military service men and women. APOs are technically under the power or supervision of the Postmasters or New York or San Francisco and are different from their overseas components called MPOs (Military Post Offices) which operate at US Military Bases for all branches of the US Military (i.e. Army, Navy, Air Force & Marines).

BMEU (Business Mail Entry Unit)

The Bulk Mail Entry Unit is where you (i.e. we) enter (non-retail) discounted First-Class and Marketing (Bulk) Mail. There are only about 2,500 BMEUs in the US, and they are not always “right next door”. The USPS® has a nifty BMEU locator. With the exception of EDDM® discounted mail, all other permitted USPS® discounted mail must be entered at a BMEU window.

BPM (Bound Printed Matter)

If you are mailing a product catalog, book or directory (weighing between 1 lb and 15 lbs.) that has “permanently bound sheets” and contains 90%+ advertising, promotional, informational, etc. content, that’s Bound Printed Matter. Phone books used to be mailed at BPM postage rates. In the internet age, CRST finds that BPM is used mostly for product guides such as automotive parts, plumbing supplies, theatrical or rigging products, etc.

BRM (Business Reply Mail®)

A type of mail whereby the recipient doesn’t have to pay for postage, and the sender/receiver pays the postage.


Bundles applies to discounted mail preparation for both Letters and Flats. Preparation for Flat-rate bundles can be different from that of Letter-rate bundles. If you are reading postal dictionary, you’re probably not a commercial mailer; in that case, your letter-rate mailing might be a non-barcode, but addressed presort mailing, a DMM or a saturation, Simplified Address mailing.

CASS™ (Coding Accuracy Support System)

You will here of CASS in context of “CASS Certification”. This means that a given address has been “ZIP+4 verified” to be recognized by the US Postal Service®.

CR / CRRT (Carrier Route)

Each USPS® location uses Carrier Routes, be it Rural (Carrier) Routes, City (Carrier) Routes, etc. As a ZIP Code grows (such as Phoenix or Las Vegas or Sarasota), the Postal Service adds more (or reassigns) carrier routes. For most people, you may need to know that there are discount postage rates applicable to the percentage of households or businesses reached within a given CR.. Example: ECRWSS (Enhanced Carrier Route Walking Sequence Saturation) means that everyone gets a piece of carrier route mail, and for most mailings, this is the best postage discount rate available. Here’s the Postal Explorer link for more info about Carrier Route mailings.

CRM (Courtesy Reply Mail)

A CRM envelope is one whereby the recipient has to put a stamp on the envelope to send it back. Such envelopes (also called CREs, or, Courtesy Reply Envelopes) are often sized #9, # 6 3/4, A2, etc. The recipient pays the postage, not the sender (contrast this with BRM, Business Reply Mail).

DDU (Destination Delivery Unit)

Similar to ADC or AADC (check their postal dictionary definitions above), you likely just need to know about DDU as it pertains to a pricing classification of mail (for flats or parcels, but no longer letters) entered at the “destination delivery unit” (i.e. DDU) for local ZIP Code delivery only. The reduced postage for such entry is sometimes called a “DDU discount”. You get this super postage discount because you would be doing the post office’s work for it — you are taking the mail directly to the local 5-digit ZIP Code post office; hence, the USPS® gives you an even bigger break on postage over other rate tiers. Not all post offices accept DDU entry discounts, so it helps to call ahead to ensure that there will be no problems.

DMM® (Domestic Mail Manual)

The DMM contains all the mailing standards and prices of the United States Postal Service® It is actually no longer printed, but may be found online at this link. There is also the Postal Explorer which has a link to the DMM and also contains other useful postal references.

DPV® (Delivery Point Validation)

You might be familiar with ZIP+4, but DPV takes ZIP+4 one step further. ZIP+4 mainly confirms recognition that the address exists, but DPV for same address confirms further that you may send mail there. In case you’d like to know more, here’s a good overview

ECRWSS (Enhanced Carrier Route Walk Sequence)

ECRWSS is the description for a discounted postage rate class of mail whereby — for a given carrier route — your presented mailing has at least 90% of all residential addresses (on the route), or, at least 75% of all business and residential addresses (on the route) prepared (as letters or flats) in house-by-house order so that a postman may deliver the mail in the order as he or she “walks” the route.

EDDM® (Every Door Direct Mail™)

EDDM® is a program rolled out by the USPS® to allow customers to present qualifying “Flats-rate” mail with “Simplfied Addressing” (e.g. “Local Postal Customer” to select carrier routes within a specific post office. It is used most commonly (as of 2018) by Realtors and small businesses, the latter whose audiences are within tight proximity to a brick and mortor store location. It is generally NOT used for non-profits and does not represent an optimal tool for fund-raising or even discounted postage. For USPS® intel (e.g. EDDM® sizes, prices, mapping tool, etc.), click on the link.

FCM (First-Class Mail®)

Perhaps the most important things to know about First-Class Mail are (a) internal standards for FCM delivery are higher than those for “lower” service mail classes such as Marketing Mail, Parcel mail, Non-Profit Org qualifying mail, etc. Except for Prioriity Express Mail, it’s the USPS®’s fastest delivery service classification Both First-Class Mail and Priority Mail have internal delivery standards of 1 – 3 days delivery.

FIM (Facing Identification Mark)

There are five types of FIMs used, but the most common FIM is the “FIM A” which is used for Courtesy Reply Envelopes. In the case of the FIM A, these five lines (technically a binary code) at the top, center right of the envelope or return postcard give the USPS® a head’s up that the mail piece is automation-compatible but that sender will be paying the postage (probably a stamp). Also, it’s a USPS® requirement that if you are claiming automation discounts for the “outside” addresses mail, any items on the “inside” also must be designed in consideration for eventual automation handling. The second most common FIM is a “FIM C” which is absolutely necessary for BRM (Business Reply Mail). A FIM C gives the destination post office that the handling of these return cards will be different than other First-Class returned mail, and that there will be additional charges paid by the recipient (and not the sender).


The Postal Service® uses the word “flats” generally to refer to large envelopes, newsletters, and magazines. For a mailpiece to qualify as a “flat”, it must be at least ONE of these things: taller than 6 1/8 “, or, longer than 11″ 1/2, or, thicker than 1/4”. You can view flats postage rates here.

HCR (Highway Contract Route)

HCRs are similar to RRs (Rural Routes). They are typically a rural area “route of travel” served by a postal contractor to carry mail over highways between designated points. Formerly called “Star Route”, an archaic rural delivery term no longer in use.

IMb™ (Intelligent Mail® barcode)

The IMb™ replaces the DP (Delivery Point Barcode), sometimes referred to as the “picket fence” barcode. The IMb™ is important because it has self-contained representation for the USPS® mailer (i.e. Mailer ID), mail class (e.g. First-Class or Bulk Mail), a mail piece ID number (“serial number”) and the mail piece (routing) destination. If you want to know more, visit this link.

IMM® (International Mail Manual)

Most people use the IMM for correct use of foreign country names. There are also some useful notes in the IMM about what-you-can-mail to each country.

IMpb (Intelligent Mail® package barcode)

(a) it’s a requirement for all parcels shipped within the USPS®, making everything trackable within the USPS® and (b) it can deliver back to the USPS® advanced data quality information rendering penalties against a mailer for missing automation quality thresholds.

Indicia (postal permit mark or box)

For large volume mail, we typically use a pre-printed postal permit box at the upper right hand corner of an envelope, flat, etc. to show the USPS® (a) the class of mail and (b) that postage has been pre-paid for the mailing. The alternative for using an indicia would be to use First-Class Mail stamps, pre-cancelled stamps or a meter mark. If you are designing a mail piece, you must have the indicia positioned at a right angle trajectory from the address block (be it a Simplified Address or “real” address).


The class of mail referred to as “Letters” means mailpieces that are between 3 1/2″ and 6 1/8″ tall, 5″ and 11 1/2″ long, and between 007″ and 1/8″ thick. Examples of Letter-rate mail are #10, #9 or #6 3/4 size business envelopes, and the “A” size envelopes (A8, A7, A6, A2, etc.).

NCOA™ (National Change of Address)

The NCOA service, by connecting with the USPS® NCOALink database of approx. 160 million change-of-address names/addresses, provides detail on the movement of people and businesses around the United States and its territories who requested to have such updates on record. Consequently, the NCOALink database gets updated constantly. Mailers at the consumer level often have confusion here because they think that the USPS® is tracking everyone that moves through the National Change of Address program.

NDC Presort price (Network Distribution Center Presort price)

The only thing you need to know about NDCs is that there is a unique presort discount rate available to mailers who wish to present their mailings directly to a USPS® NDC. It could be that your closest postal center IS an NDC although there are only 22 of them presently in the US and they tend to be in metropolitan areas. You may find the listing for all NDCs here.

PAVE™ (Presort Accuracy Validation and Evaluation)

Essentially, this term in our postal dictionary refers to the process that the USPS® uses with private industry to assess mailing software for address handling quality. Software developers and providers must prove to the USPS® that their code is top notch, and therefore worthy of PAVE certification.

PCSC (Pricing and Classification Service Center)

Located in New York City, the PCSC is the Postal Service®’s decision bureau for evaluating (and ruling upon) many USPS® domestic and foreign pricing as well as extending privileges such as not-for-profit eligibility and periodicals privileges.

PO Box (Post Office™ Box)

Two things to know here: first, PO Boxes are different than “Boxes”. If you don’t use PO Box with a number (and sometimes the legacy letter), then the “Box” might not mean a Post Office box. There are private boxes and the distiction is important. Second, some towns, in whole or in part, use PO Boxes in lieu of getting mail at a street address. Therefore, having the street address might not be very helpful for mailing — having a PO Box in any circumstance is the best most reliable way to ensure deliverability.


Presort is the process by which a mailer prepares mail so that it is sorted to at least the finest extent required by the standards for the price claimed. Generally, presort is performed sequentially, from the lowest (finest) level to the highest level, to those destinations specified by standard and is completed at each level before the next level is prepared. Not all presort levels are applicable in all situations.

PRSRT STD (Presorted Standard Mail)

This is another way of saying “Bulk Mail”. It has also been called Third Class Mail, Advertising Mail, Standard Mail, Standard “A” mail. As of 2017, it’s now “Marketing Mail”. This is a discounted class of mail under which non-profit (not-for-profit) mail also falls. Click link for more information.

PS (Postage Statement)

A postage statement is what you fill out when you want to present mail (letters, parcels or flats) at discounted postage rates. Here is the USPS® link to all postage statements. Notice how they all start with “PS Form”. If you wish to do a regular bulk mailing, and have the correct permit(s) in place, then you would probably be using a PS 3602-R

RR (Rural Route)

Rural Routes are needed when preparing mail for post offices that have rural route delivery. Even Westchester County NY, a largely metropolitan area with many City Routes, has Rural Routes in the northern part of the county. If you are preparing a saturation mailing to a ZIP Code with rural routes, you will need to know the RR number and the number of deliverable addresses on the route. Here’s a link to get such counts if you are preparing your own mail. Less often, you may see occasionally see an address that looks like this: “RR [#] BOX [###]”. Many states have retired this type or rural addressing simply because emergency services organizations can’t send an ambulance or fire truck to such locations.

RTS (Return-To-Sender)

You will see this handwritten by a postal carrier as “RTS” on returned mail, mostly for First-Class Mail. The carrier is supposed to put down why the mail piece is being returned, but we find this is rarely done, or at least rarely done legibly. Common RTS reasons are NFA (No Forwarding Address), NSA (No Such Address), NMR (No Mail Receptical, such as a mailbox) or simply “Refused” or “Deceased”.

SCF (Sectional Center Facility)

A Sectional Center Facility (SCF) is typically both a major mail entry and a mail handling point within the USPS® network, and usually has a BMEU (Business Mail Entry Unit) window “attached” (on site) to receive bulk mailings. There are approximately 350 SCFs around the U.S. and the rates for ZIP entry are better than those for DNC entry, but not as good as DDU. A conventional SCF “oversees” the distribution for other ZIP Codes and serves as the regional collection point for same 5-Digit ZIP Code Post Offices. SCFs are especially important for discounted mail purposes because the correctly presented SCF entry mailing, over another perhaps more convenient BMEU window entry, can offer a significant postage rate discount. Here is a list of current SCFs and note, too, that state lines don’t always matter in the logistics of SCF mail handling (and, changes are not uncommon).

Simplified Address

Simplified Addresses typically look like “Postal Customer”, “Postal Patron”, “Current Resident”, “Current Boxholder”, etc. This form of “addressing” is a confusing term for some because there’s no real address here. It’s used for saturation mailing purposes so that “everyone gets one” for PO Boxes (explained above in our postal dictionary) or mailing routes.

ZIP Code™ (Zone Improvement Plan Code)

In 1963 the USPS® rolled out the ZIP Code™ requirement for domestically addressed mail. The volumes were too much now not to have a numeric value to help postal employees sort the mail.


3-Digit refers to the first three (3) numbers in a 5-Digit ZIP Code. Common uses for the 3-digit term apply to 3-digit presort prepartion for letters/flats bundling as well as setting up ADC or AADC destination trays or sacks (for letters or flats, respectively).


All ZIP Codes have 5-Digits, but the term is typically referred to in consideration of presorted mail preparation, not unlike 3-Digit bundle/tray preparation.

Our postal dictionary will be updated regularly with newer and increasingly more popular mailing terms.

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.

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