Short answer
When the Postal Service cannot deliver a piece as addressed, it marks the piece with the reason and sends it back. USPS calls that marking an endorsement, and the full list is Exhibit 1.4.1 in section 507 of the Domestic Mail Manual. Attempted Not Known means “Delivery attempted; addressee not known at place of address.” No Such Number means “Addressed to nonexistent number and correct number not known.” Vacant is meant for mail addressed to “Occupant.” Moved, Left No Address means the addressee “moved and filed no change-of-address order.” The exhibit lists 25 endorsements in all, including two that apply only to mail sent to a commercial mail receiving agency (CMRA), such as a mailbox store: “Undeliverable as Addressed, Missing PMB or # Sign” and “Delivery Suspended to Commercial Mail Receiving Agency.”
Key takeaways
- The reason printed on a returned piece is called an endorsement. DMM 507.1.4.1 says undeliverable-as-addressed mail “is endorsed by the USPS with the reason for nondelivery,” and Exhibit 1.4.1 lists 25 of them.
- Attempted Not Known is about the name, not the street. The manual’s wording is “Delivery attempted; addressee not known at place of address.” The address can exist and still produce this return.
- Vacant has a limit written into the manual. The exhibit describes it as “House, apartment, office, or building not occupied” and adds “(Use only if mail addressed “Occupant.”)”
- Two endorsements apply only to mail sent to a commercial mail receiving agency (CMRA), such as a mailbox store: “Undeliverable as Addressed, Missing PMB or # Sign” and “Delivery Suspended to Commercial Mail Receiving Agency.” Mail to a CMRA without the private mailbox (PMB) or # designation can come back marked “Undeliverable as Addressed, Missing PMB or # Sign” under DMM 508.1.8.3.
- A piece returned as undeliverable or refused generally cannot be dropped back in the mail. DMM 508.1.1.6 says it may not be remailed unless it is placed in a new envelope or wrapper with a correct address and new postage. A piece returned only for short postage can take the added postage on the original piece.
Before you start
- Keep the returned piece and read the reason exactly as printed. The wording maps to one line in the table below.
- Have the full address you used on hand, including any suite, unit, private mailbox (PMB), or # number.
Who this is for
- Business owners whose letters to customers, vendors, or agencies came back with a reason printed on them.
- Anyone who received their own mail back, or saw a return scan in tracking, and wants to know what the words mean.
Where the reason on a returned envelope comes from
The words on a returned envelope are an endorsement. The Domestic Mail Manual (DMM), section 507.1.4.1, says undeliverable-as-addressed mail “is endorsed by the USPS with the reason for nondelivery as shown in Exhibit 1.4.1.” That exhibit gives each reason a fixed meaning.
The same section says such mail “is forwarded, returned to the sender, or treated as dead mail, as authorized for the particular class of mail.” The manual prints some endorsement names with a dash between two parts, such as Attempted and Not Known. We write them without the dash below.
One of the top Google results for “usps return to sender attempted not known,” in the results we saved on September 30, 2026, is an archived 2003 edition of the manual (DMM F010). The current list is the one in DMM 507, and it is the one we quote here.
The return reasons, decoded
The first two columns come straight from Exhibit 1.4.1. The last two columns are our suggestions for what to check. They are not USPS rules.
| Endorsement | What DMM 507 Exhibit 1.4.1 says | If you sent it, check | If it was addressed to you, check |
|---|---|---|---|
| Attempted Not Known | “Delivery attempted; addressee not known at place of address.” | The recipient’s exact name or business name, and any suite or unit number. | Whether the name on the mail is one that receives mail at that address, and whether your suite or unit is on it. |
| No Such Number | “Addressed to nonexistent number and correct number not known.” | The street number against the recipient’s current records. | How your street number appears in USPS data before you give it out again. |
| No Such Street | “Addressed to nonexistent street and correct street not known.” | The street name, spelling, and city. | The exact street name as USPS lists it. |
| Insufficient Address | “Mail without number, street, box number, route number, or geographical section of city or city and state omitted, and correct address not known.” | Which element is missing from the address you used. | That every place that mails you has the full address. |
| Illegible | “Address not readable.” | The print quality and placement of the address. | Nothing on your side, unless you wrote the address for the sender. |
| Vacant | “House, apartment, office, or building not occupied. (Use only if mail addressed “Occupant.”)” | Whether the piece was addressed to “Occupant.” If it carried a name, ask the delivering Post Office why this reason was used. | Whether the address is flagged as vacant in USPS data, which is a separate record from this endorsement. |
| Moved, Left No Address | “Addressee moved and filed no change-of-address order.” | Whether you have a newer address for this person or business. | Whether you filed a change-of-address order when you moved. |
| Not Deliverable as Addressed, Unable to Forward | “Mail undeliverable at address given; no change-of-address order on file; forwarding order expired.” | The address you have on file. The envelope does not say which of the three causes applies. | Whether your forwarding order has expired. |
| Temporarily Away | “Addressee temporarily away and period for holding mail expired.” | Whether to resend later. | The end date of your mail hold. |
| Refused | “Addressee refused to accept mail or pay postage charges on it.” | Whether the recipient still wants mail from you. | Nothing, if you meant to refuse it. |
| Unclaimed | “Addressee abandoned or failed to call for mail.” | Whether the recipient knew a piece was waiting for pickup. | Pickup notices left at your address or mailbox. |
| Deceased | “Used only when known that addressee is deceased, and mail is not properly deliverable to another person.” | Your records for this person. | Not applicable. |
| No Mail Receptacle | “Addressee failed to provide a receptacle for receipt of mail.” | Whether another address is on file for the recipient. | That your address has a mailbox or other receptacle. |
| Box Closed, No Order | “Post office box closed for nonpayment of rent.” | Whether the recipient has a new address. | The rent status of your PO box. |
| Undeliverable as Addressed, Missing PMB or # Sign | “Failure to comply with 508.1.8.3d.” | That the address includes the PMB or # number the recipient gave you. | That every sender has your PMB or # number in the address. |
| Delivery Suspended to Commercial Mail Receiving Agency | “Failure to comply with 508.1.8.1 through 508.1.8.4.” | Whether the recipient has another address. | Your mailbox provider, and whether your PS Form 1583 is on file with it, since the cited sections set rules for both the agency and its customers. |
| Returned for Postage | “Mail without postage or indication that postage fell off.” | The postage on the piece. | Not applicable. |
Source: USPS Domestic Mail Manual 507, Exhibit 1.4.1, read September 30, 2026. The exhibit lists 25 endorsements. The eight not shown here are “In Dispute,” “No Such Office in State,” “Outside Delivery Limits,” “Returned for Better Address,” “Returned to Sender, Mailpiece Contains Nonmailable Contents,” “Returned to Sender Due to Addressee’s Violation of Postal False Representation and Lottery Law,” “Returned to Sender Due to Addressee’s Violation of Postal False Representation Law,” and “Returned to Sender Due to Addressee’s Violation of Postal Lottery Law.”
Two rows carry extra detail in the manual. For Deceased, the exhibit says the endorsement “must be made personally by delivery employee and under no circumstance may it be rubber-stamped.” For Vacant, the note limiting it to “Occupant” mail is part of the exhibit’s own text.
The Insufficient Address row has its own guide: what to do when USPS says Insufficient Address but the address is correct.
Why mail can come back when the address is correct
Several endorsements have nothing to do with the street address itself. Attempted Not Known is about the addressee, and Moved, Left No Address, Refused, Unclaimed, Temporarily Away, and Deceased are about the person or business. A correct street address can still produce any of them.
The carrier also does not look up a better address for most mail. DMM 507.1.3 says carrier offices give directory service only to certain types of mail, such as certified, collect on delivery (COD), and registered mail and parcels at Package Services or Parcel Select prices, and it adds that “USPS does not compile a directory of any kind.” For an ordinary letter, the address on the piece is what the carrier works from.
A change-of-address order also shapes what comes back. Under Exhibit 1.5.1, a First-Class Mail piece with no mailer endorsement gets the same treatment as “Forwarding Service Requested.” With no order on file, it is returned with the reason attached. With an order on file, it is forwarded in months 1 through 12, returned with the new address attached in months 13 through 18, and returned with the reason attached after month 18. Our guide to how long USPS forwards mail covers those clocks in detail.
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Return to Sender in tracking, and where the reason is
Tracking pages show short scan events. We did not find a definition of the phrase Return to Sender Processed in DMM 507 or 508, so we will not tell you what each tracking line means.
What the manual does say helps. A return is one of the three outcomes 507.1.4.1 lists for undeliverable mail, and the reason for it is the endorsement on the piece. The sender reads the reason on the returned piece itself.
If you sent a tracked package and want it redirected, the DMM describes Package Intercept in 507.5.0. Only the sender or an authorized representative may request it, a request stays active for 7 business days, and the manual says “Interception of eligible mailpieces is not guaranteed.” A fee is charged only if the piece is intercepted, and additional postage can apply under 507.5.2. It covers tracked classes such as Priority Mail and USPS Ground Advantage, and it is not available for mail without a tracking barcode. The USPS Package Intercept page also lists items addressed to a commercial mail receiving agency (CMRA) as not eligible. DMM 507.5 does not say whether a piece already on its way back to the sender can still be intercepted.
Refusing mail and sending a returned piece again
If mail comes to you that you do not want, DMM 508.1.1.3 lets you return it after delivery: “an addressee may mark a mailpiece “Refused” and return it within a reasonable time, if the piece or any attachment is not opened.” The same section lists mail that may not be refused and returned postage-free after delivery. The list includes Registered Mail, insured mail, Certified Mail, COD, and Adult Signature pieces, and response mail to your own advertisement or solicitation that you did not refuse when it was offered.
If mail you sent comes back, DMM 508.1.1.6 says that generally, a returned piece that was undeliverable as addressed or refused “may not be remailed unless it is placed in a new envelope or wrapper with a correct address and new postage.” A piece that came back only for short postage is the exception: the missing postage can be added to the original piece.
When the returned mail is business mail
For a business, a returned piece can mean a notice from a state agency, a bank, or a customer that never reached you. The endorsement tells you which part of the address to look at. Attempted Not Known points at the name, No Such Number and No Such Street point at the street line, and Moved, Left No Address points at the records of whoever sent it.
Mailbox addresses have their own rule. DMM 508.1.8.3 says a commercial mail receiving agency (CMRA) must show its customers’ addresses with “PMB” or the alternative “#” sign, and that “The USPS may return mail without a proper address to the sender endorsed “Undeliverable as Addressed, Missing PMB or # Sign.”” If you use a mailbox address, check that every sender has the full address, including that number.
If the returned mail came from your state, compare the address the state has for your company with the one you use today. An LLC can have more than one on file, and our guide to registered agent and business addresses explains the difference. Our guide to business mail returned as undeliverable walks through fixing the address once you know the cause.
Before you give an address out again, you can look it up in our free address checker. It shows whether USPS data classifies the address as residential or commercial, whether it is flagged as a CMRA, whether it is flagged as vacant, and whether the building uses suite or unit numbers. A vacant flag in USPS data is a separate data point from the Vacant endorsement on a returned piece.
Not legal advice
This guide quotes the USPS Domestic Mail Manual sections 507 and 508 as read on September 30, 2026. The manual changes over time, and a local Post Office can explain a specific return. Ask the delivering Post Office when a reason does not match what you know about the address.
Frequently Asked Questions
Sources & References
Primary sources this guide is based on.
- 1USPS Postal Explorer · DMM 507 Mailer Services, Exhibit 1.4.1 and Exhibit 1.5.1 (accessed September 30, 2026)
- 2USPS Postal Explorer · DMM 508 Recipient Services, sections 1.1 and 1.8 (accessed September 30, 2026)
- 3USPS · USPS Package Intercept (accessed September 30, 2026)
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