The block near the stamp is a permit imprint, and it is the most informative thing on a business envelope after the return address. It names the class of mail, the post office where the mailing was entered, and a permit number belonging to whoever paid the postage. Read together, those three tell you that the sender mails in volume, where the mailing physically originated, and how much the sender was willing to spend on reaching you correctly.
Everything published on this is either a raw USPS regulation or a vendor explaining how to buy a permit. Nothing explains it to the person on the receiving end, which is a shame, because it is genuinely readable.
What the block actually contains
A permit imprint, sometimes called indicia, replaces a stamp or meter mark and usually sits in the upper right corner. Four elements appear in some arrangement:
- The class of mail, printed as PRSRT STD, PRESORTED FIRST-CLASS MAIL, FIRST-CLASS MAIL or similar
- US POSTAGE PAID, confirming postage was paid through a standing account rather than with stamps
- A city and state, which is the post office where the mailing was entered
- PERMIT NO. followed by a number, identifying the permit holder’s account at that post office
Presorted means the mailer sorted the mail by destination before handing it over, in exchange for a lower rate. Doing that is only worth the effort in volume, so a presort marking is reliable evidence that you are one of many recipients rather than the subject of an individual letter.
The single most useful thing it tells you
Mail class governs what happens when a piece cannot be delivered, and that is where real signal lives.
First-Class Mail is forwarded to a new address and returned to the sender when undeliverable, as part of what the sender paid for. Marketing Mail, the class marked PRSRT STD, is neither forwarded nor returned by default. A sender who wants either has to pay extra for an ancillary service endorsement, which is that small line reading something like ADDRESS SERVICE REQUESTED or RETURN SERVICE REQUESTED.
So the class is a statement about how much the sender cares whether the right person receives this. Something genuinely tied to your account, a bill, a notice, a legal document, will normally travel First-Class. A PRSRT STD piece with no service endorsement is telling you the sender is content for it to be discarded if you have moved.
The endorsement line, and why it is worth finding
The small line near the address reading ADDRESS SERVICE REQUESTED, RETURN SERVICE REQUESTED, CHANGE SERVICE REQUESTED or FORWARDING SERVICE REQUESTED is an ancillary service endorsement, and each buys the sender a different outcome when you have moved.
Broadly, some instruct USPS to forward the piece and tell the sender your new address, some ask only for the address correction without forwarding, and some ask for the piece back. What matters to a reader is simpler than the distinctions: the presence of any of them means the sender paid extra to keep its address file accurate about you specifically. Their absence on bulk mail means the opposite.
The permit city is not the sender’s city
This trips up almost everyone. The city in the indicia is where the mailing entered the postal system, which is the printing or mailing vendor’s location, and the postmark records the processing facility. Neither is the sender’s headquarters, and neither has to match the return address.
A letter with a Wisconsin return address, an Illinois permit city and a Nebraska postmark is describing a completely ordinary arrangement: a company, its print vendor, and the facility that handled the mail. Reading those three as a contradiction produces false alarms. The wider version of this is in why a company mails you from a state you have no connection to, and the return address itself is broken down in how to read a business return address.
Permit numbers, and their honest limit
A permit number is unique only in combination with the post office that issued it, so PERMIT NO. 100 exists in hundreds of cities. USPS does not publish a public directory mapping permit numbers to holders, and the holder is frequently the mailing vendor rather than the organization whose name is on the letter.
That makes the permit number weak as an identifier and useful as a corroborator. If two letters carry the same permit number and permit city, they were mailed through the same operation, which is a real link between two pieces of mail even when their return addresses differ.
The barcodes
The bars along the bottom or in the address block encode routing and tracking, not identity. The Intelligent Mail barcode carries the mailer identifier, a serial number and the routing code derived from your address. It is machine data for USPS and for the mailer’s own tracking, and it is not something a recipient can decode into a company name with any tool available to the public. Treat any service claiming otherwise with caution.
Putting it together on an unfamiliar envelope
Read the class first, because it separates individually addressed correspondence from bulk. Note the permit city as a lead to the vendor rather than the sender. Check whether a service endorsement was paid for, since that shows intent. Then go to the return address for identity, and to the box itself if the name is unfamiliar, using how to find out who owns a PO Box.
None of this tells you whether the contents are genuine. What it does is set your expectation before you open anything: bulk marketing, or something a sender paid to reach you specifically. If the contents then ask for money or personal information, that decision is separate, and the path is in what to do with a letter from an unknown sender.
FAQ
What does PRSRT STD mean on an envelope?
Presorted Standard, now Marketing Mail. The sender sorted the mail in bulk for a lower rate. It is not forwarded or returned when undeliverable unless the sender paid extra for that service.
Can I look up who owns a permit number?
Not through a public directory. Permit numbers are unique only per post office, and the holder is often a mailing vendor rather than the company named in the letter.
Why is the permit city different from the return address?
The permit city is where the mailing was entered into the postal system, usually the print vendor’s location. The return address is where replies go. They are different facts.
Does bulk mail marking mean the letter is junk?
It means you are one of many recipients. Legitimate organizations send genuine notices in bulk too, so it sets expectations rather than delivering a verdict.
Can the barcode tell me who sent it?
No. It encodes routing and mailer tracking data, not a publicly resolvable sender identity.
Last verified: 25 August 2026. Reviewed every 12 months, or sooner if USPS mail classes change.
Sources: USPS Domestic Mail Manual, permit imprints · USPS Postal Explorer · This site’s Editorial Policy and Disclaimer explain how identifications here are sourced.
