How to Improve Direct Mail Deliverability: Key Strategies for Success

Direct mail deliverability is the share of your mailing that reaches a real, current address where the intended person can pick it up. It is a physical-mail problem, decided by the quality of the address data, the postal processing applied to it, and the endorsements printed on the piece. Every one of those is in your control before the mail date.

This guide walks through that stack in the order the work happens, from CASS and NCOA through DPV, presort and Intelligent Mail barcode accuracy, undeliverable-as-addressed handling, list age, dedupe, suppression, and Informed Delivery. It ends with a pre-drop checklist and the two numbers that tell you whether the work paid off.

What deliverable means in physical mail

USPS delivers to delivery points, not to people. A piece is deliverable when the address resolves to a specific, active delivery point in the USPS database and the addressee still receives mail there. It fails when the address does not exist, sits vacant, or belongs to someone who moved.

USPS calls a failed piece Undeliverable As Addressed, or UAA. Depending on mail class and endorsement, a UAA piece is forwarded, returned to you, or disposed of, and unendorsed USPS Marketing Mail is disposed of with no notice to you. That is why deliverability has to be engineered before the drop rather than measured after it.

Step 1: CASS standardization and address matching

CASS stands for Coding Accuracy Support System, the USPS program that certifies address-matching software (CASS certification, PostalPro). A CASS-certified process corrects and standardizes each address to USPS format, confirms the ZIP Code, and appends the ZIP+4, delivery point code, and carrier route. Those codes are what the presort and the Intelligent Mail barcode are built from, so CASS is the first step for anything that will mail at automation rates.

CASS catches the address problems that look fine to a human: a street suffix that is wrong, a missing directional, a unit number in the wrong field, a city name that does not match the ZIP Code. Records that cannot be coded come back flagged instead of mailing blind. The run is documented on the CASS Summary Report, PS Form 3553, which accompanies presorted mailings. Our CASS certification guide covers the coding in detail.

Step 2: NCOA and the 95-day Move Update rule

Standardizing an address does not tell you whether the person still lives there. That is what National Change of Address processing does. We run National Change of Address (NCOA) processing against the USPS 48-month mover file. NCOALink is one of the approved methods under the USPS Move Update standard, DMM 602.5 (pe.usps.com), which requires addresses on presorted First-Class Mail and USPS Marketing Mail to be updated within 95 days of the mailing date.

NCOA matches your records against change-of-address filings and returns the new address when the mover left one, or a flag to suppress the record when no forwarding address exists. It updates addresses; it does not delete them. On a typical commercial list we see 6 to 9 percent of records flagged as moved, and the older the file, the higher that number runs.

The 95-day rule is a compliance deadline, not a suggestion. If your last NCOA pass is more than 95 days old on the mail date, the mailing is out of compliance with Move Update, which puts the automation postage discount at risk and can trigger a per-piece assessment. Re-run NCOA inside the window before every drop. Our NCOA explainer covers the 18-month versus 48-month difference and the documentation.

Step 3: DPV validation

ZIP+4 coding confirms that an address falls within a valid range. Delivery Point Validation goes one step further and confirms that the specific address is an actual delivery point USPS serves (DPV overview, PostalPro). The difference matters on new subdivisions, large apartment buildings, and rural routes, where an address can code cleanly to a ZIP+4 and still not exist.

DPV also returns indicators you can act on: vacant addresses, addresses USPS does not deliver to, and missing or invalid secondary numbers such as an apartment or suite. On a typical B2C list, about 94% of records pass CASS/DPV validation; of those validated records, about 98.5% are deliverable after NCOA processing. Our address verification services run CASS, NCOA, and DPV as one pass on every job.

Step 4: Presort and Intelligent Mail barcode accuracy

Deliverability is not only whether the address is right. It is also whether the piece is routed right. Presort software uses the ZIP+4 and delivery point codes from CASS to sort the mailing into trays and sacks by destination, and the Intelligent Mail barcode (IMb overview, PostalPro) printed on each piece carries the routing code, your mailer ID, and a serial number that USPS scanners read at every step.

Two accuracy problems show up here. A barcode built from a stale or uncoded address routes the piece to the wrong tray, where it is handled as an exception and arrives late or not at all. A barcode printed outside its size or clear-zone tolerance does not scan, and the piece drops to manual handling. Our IMb requirements guide covers the print specs, and our presort services handle the sortation and file the electronic documentation with USPS.

Full-service IMb also gives you something no other step does: visibility. Each unique barcode produces scan events as the piece moves through the network, which is how you measure delivery instead of assuming it. We present our own mail on our permit at the Lakeland BMEU, so scan data starts the day the mail leaves our building.

Step 5: Undeliverable-as-addressed handling and endorsements

Some pieces will still fail, and what happens to them is decided by the ancillary service endorsement printed on the piece under DMM 507, Mailer Services (pe.usps.com). The endorsement tells USPS whether to forward the piece, return it, or dispose of it, and whether to send you the new address. Without one, First-Class Mail is forwarded or returned during the forwarding period at no added charge, and undeliverable USPS Marketing Mail is disposed of.

• Address Service Requested. The piece is forwarded when a forwarding order exists, and you receive a separate notice of the new address. Undeliverable pieces come back to you with the reason.
• Return Service Requested. The piece is not forwarded. It is returned to you with the new address or the reason for nondelivery. Best for time-sensitive offers and for cleaning a house file.
• Change Service Requested. The piece is not returned. You receive the new address or the nondelivery reason as a separate notice, and USPS disposes of the piece. The lowest-cost way to harvest corrections on large Marketing Mail drops.
• Forwarding Service Requested. The piece is forwarded during the forwarding period and returned with the reason if it cannot be delivered. You do not receive a separate notice of the new address.

Fees for forwarding, returns, and notices vary by mail class and are listed in DMM 507, so pick the endorsement based on what you will do with the information. When the mailing carries a full-service IMb, corrections arrive electronically through Address Change Service (ACS), which is how they get back into your list before the next drop. Our undeliverable mail guide lists the UAA reason codes.

Step 6: List age, dedupe, and suppression

List age

Address quality decays every month a list sits untouched, because people move, businesses close, and buildings change, so a list that was clean last year is not clean now. Treat the NCOA date, not the purchase date, as the list's age, and re-run hygiene inside the 95-day window before every mailing. For house files, quarterly NCOA is the usual cadence; for rented prospect lists, ask the list provider for the hygiene date and run your own pass anyway.

Dedupe

Duplicates are a deliverability problem as well as a cost problem, because two pieces to one household read as carelessness to the recipient. Dedupe after CASS standardization, not before, so that two spellings of the same apartment resolve to the same record. Decide up front whether you are deduping to the individual, the household, or the business address, because each rule produces a different count. Our list cleaning guide walks through the merge/purge sequence.

Suppression

Suppression removes records you could deliver to but should not mail. The usual suppression files are your own do-not-mail list, deceased records, prior responders who should get a different piece, vacant and no-stat addresses from DPV, and, for consumer prospecting, the industry opt-out list maintained by the ANA. Every suppression is a piece you do not pay to print or mail.

Informed Delivery as a visibility layer

USPS Informed Delivery emails enrolled households a grayscale image of the letter-size mail arriving that day (Informed Delivery for business mailers, usps.com). For a mailer it confirms delivery to the household on the day it happens, and it lets you attach a color image and a link next to the scan, so the piece gets a digital impression before anyone opens the mailbox.

Informed Delivery does not make a bad address deliverable. It rides on the same Intelligent Mail barcode and address data as the rest of the stack, which means a mailing with clean data and full-service IMb qualifies with no extra list work. Our Informed Delivery guide covers campaign setup and the current postage incentives.

How to measure deliverability

Two measurements tell you whether the stack worked, and you need both because each one is blind to something.

• UAA rate. Returned and notified pieces divided by pieces mailed. This only counts what USPS reports back, so it depends on the endorsement you printed. An unendorsed Marketing Mail drop reports a UAA rate of zero no matter how bad the list was.
• IMb scan rate. The share of pieces that received a final processing scan inside the expected delivery window. This is the closest thing physical mail has to a delivered receipt, and it catches the pieces that vanished without a return.

Read the two together. A low scan rate with a low UAA rate means pieces are failing silently, which is usually a list-age problem. A high UAA rate with a healthy scan rate means the endorsement is doing its job and the list needs suppression updates.

Track both by list source, and the sources that underperform become obvious after two drops. Our direct mail tracking service reports scan data by piece and by segment next to the response data for the same mailing.

Pre-drop deliverability checklist

1. Export the list with street, city, state, and ZIP in separate fields, plus a unique record ID.
2. Run CASS standardization and keep the PS Form 3553 with the job.
3. Run NCOA against the 48-month file within 95 days of the mail date. Update movers and suppress records with no forwarding address.
4. Run DPV. Remove or hold vacant, no-stat, and invalid-secondary records.
5. Dedupe on the standardized address using the rule you chose: individual, household, or business.
6. Apply suppression files: do-not-mail, deceased, prior responders, and opt-outs.
7. Choose the ancillary service endorsement that matches what you will do with corrections, and print it in the correct position.
8. Presort from the coded file and print a full-service IMb on every piece inside the size and clear-zone tolerances.
9. Proof a sample of live records for address block format, barcode placement, and window alignment.
10. After the drop, log the UAA rate and the IMb scan rate by list source, and feed corrections back into the file.

Mail Processing Associates has run this stack on customer lists since 1989 from a single Lakeland, Florida facility that serves businesses in all 50 states, and every list we handle is processed under SOC 2 Type 2 audited controls. Send us your list and your mail date, and we will run the hygiene, show you the exception counts, and quote the job with the deliverability work built in.

Frequently asked questions

What is a good direct mail deliverability rate?

After CASS, NCOA, and DPV on a typical B2C list, about 94% of records pass validation, and of those validated records about 98.5% are deliverable after NCOA processing. An unverified list that is a year old runs well below that. Watch the trend by list source across drops rather than one campaign's figure.

Does email deliverability advice apply to direct mail?

No. Nothing that decides whether an email is delivered has any effect on a physical mailpiece. Direct mail deliverability depends on address accuracy (CASS and DPV), move updating (NCOA), routing accuracy (presort and the Intelligent Mail barcode), and the endorsement that controls what happens to a piece that cannot be delivered.

How often do I need to run NCOA?

Within 95 days of every mail date for presorted First-Class Mail and USPS Marketing Mail, under the USPS Move Update standard in DMM 602.5. Most house files run NCOA quarterly, and high-frequency mailers run it monthly.

What is the difference between CASS and DPV?

CASS standardizes the address and assigns the ZIP+4, delivery point, and carrier route codes. DPV confirms that the specific address is a real delivery point USPS serves. An address can pass CASS and fail DPV, which is why both run on every list.

Which ancillary service endorsement should I use?

Use Address Service Requested when you want the piece delivered and the new address reported, Return Service Requested when the offer is time-sensitive and you want the piece back, and Change Service Requested when you want corrections at the lowest cost and do not need the piece returned. Fees vary by mail class under DMM 507.

Does better address data improve response?

Yes, in the plain sense that a piece that never arrives cannot respond. Beyond that, the same hygiene that improves deliverability also improves targeting, because vacant, duplicate, and moved records are removed before you pay to print and mail them.