The U.S. Postal Service’s rules and regulations decide what you’re allowed to mail, how you have to pack and label it, when a postal inspector can open your package, and what you can recover if something is lost, damaged, or stolen. The rules below are the ones that carry real consequences — fines, criminal penalties, seized packages, or denied claims — for anyone who sends or receives mail.
What You Can and Can’t Mail
USPS separates items into three groups: freely mailable, restricted, and prohibited. Prohibited items include illegal narcotics and certain explosives. Knowingly mailing something the law declares nonmailable carries up to one year in federal prison and a fine. Mailing a banned item with intent to harm a person or damage property jumps to up to twenty years, and if someone dies as a result the statute authorizes a life sentence or the death penalty.1Office of the Law Revision Counsel. 18 U.S. Code 1716 – Injurious Articles as Nonmailable
Restricted items can ship, but only under narrow conditions. Firearms, tobacco products, and certain alcoholic beverages move through the mail only when sent by authorized parties who meet verification and packaging requirements spelled out in the Domestic Mail Manual.2United States Postal Service. Domestic Mail Manual Skipping those steps triggers civil penalties starting at $250 and reaching up to $100,000 per violation, plus cleanup costs when hazardous materials are involved.3GovInfo. 39 U.S. Code 3018 – Hazardous Material
The sender is fully responsible for knowing which category a shipment falls into. USPS can inspect and seize any non-compliant package. The most common trap is the gap between consumer-grade and professional-grade versions of the same product — a household cleaner may ship fine while its industrial version requires full hazmat handling.
Hazardous Materials and Labeling
Plenty of everyday items count as hazardous materials under postal rules. Lithium-ion batteries in electronics, alcohol-based perfumes, aerosol sprays, and mercury-containing devices all fall under the mailing standards in 39 CFR 113 and USPS Publication 52.4Government Publishing Office. 39 CFR 113 – Hazardous, Restricted, and Perishable Mail The sender has to identify them clearly on the package so handlers can route them safely.
The labeling system changed at the end of 2020. Since January 1, 2021, the only acceptable marking for eligible limited-quantity consumer goods shipped by ground is the DOT limited quantity mark, a plain square-on-point diamond. The older ORM-D marking is gone.5Postal Explorer. DMM Advisory – Elimination of the ORM-D Category Wrong label or no label at all pulls the package for inspection.
Air-eligible versus ground-only is the other distinction that matters. Aerosols, highly flammable liquids, and anything with a low flashpoint generally cannot fly and must travel by surface transportation. Before mailing anything you suspect is hazardous, check the product’s safety data sheet against Publication 52 — that document controls what can fly, what stays on the ground, and what can’t ship at all.6United States Postal Service. Publication 52 – Hazardous, Restricted, and Perishable Mail
Size, Weight, and Addressing Rules
Most domestic packages are capped at 108 inches in combined length and girth. Only certain ground services — USPS Ground Advantage (commercial) and Parcel Select — accept pieces up to 130 inches, at oversized pricing.7Postal Explorer. Quick Service Guide 201e – Minimum and Maximum Sizes No mailpiece can exceed 70 pounds regardless of dimensions, and some mail classes have lower weight limits.8Postal Explorer. Minimum and Maximum Sizes Anything over is returned or held for pickup.
Addressing follows a set layout. Delivery address goes centered on the largest face of the package, return address in the upper left corner. Certain mail classes require additional markings indicating the service level or contents. All markings must be legible and placed away from stamps or barcodes so scanning equipment reads them cleanly.
Media Mail: Cheaper Rate, Fewer Rights
Media Mail is significantly cheaper, and there are two catches. First, the list of eligible contents is narrow: books of at least eight pages, sound and video recordings, printed music, playscripts, manuscripts, film, computer-readable media with prerecorded information, and printed educational reference charts.9United States Postal Service. Media Mail Service If it’s not on that list, it doesn’t qualify. The most common disqualifier is advertising; Media Mail packages cannot contain ads, aside from a narrow exception for incidental announcements of other books inside a book or other recordings inside a sound recording. Merchandise, electronics, clothing, and general brochures all fail.
Second, using Media Mail counts as your consent to inspection.10Postal Explorer. 170 Retail Mail – Media Mail and Library Mail Postal employees can open the package whenever they have reason to suspect the contents don’t match the rate. A small, heavy box claiming to hold books tends to draw a second look. If it fails inspection, you either owe the difference in postage at the correct rate or the package goes back to you.
When USPS Can Open Your Mail
First-Class letters and sealed packages carry full Fourth Amendment protection. Postal inspectors need a warrant based on probable cause before opening any First-Class mail.11United States Postal Inspection Service. USPIS FAQs Media Mail, Library Mail, and other non-sealed classes do not get the same shield and can be opened without a warrant because they are not treated as private correspondence.
Even sealed First-Class mail isn’t beyond outside examination. Inspectors can always observe the shape, weight, return address, and any odors or anomalies. If wires are protruding, something is leaking, or there is an immediate threat to safety, they can act without a warrant under an emergency exception. Short of that, sealed mail stays sealed unless a judge signs off.
Mailbox Installation and Protection
Residential curbside mailboxes have to meet USPS installation standards. The bottom of the box or the point of mail entry sits between 41 and 45 inches above the road surface, and the front face is set back 6 to 8 inches from the curb.12United States Postal Service. How to Install a Mailbox If you don’t have a raised curb, your local postmaster can advise on placement. These measurements let the carrier reach the box safely from the vehicle.
Once installed for mail receipt, the box becomes federally protected property. Willfully damaging or destroying a mailbox, or the mail inside it, is a federal crime carrying up to three years in prison and a fine of up to $250,000.13Office of the Law Revision Counsel. 18 U.S. Code 1705 – Destruction of Letter Boxes or Mail14United States Postal Inspection Service. Mailbox Vandalism Only the owner and authorized postal carriers may access the interior.
A separate federal rule makes it illegal to place anything without postage inside a mailbox to avoid paying for postage.15Office of the Law Revision Counsel. 18 U.S. Code 1725 – Postage Unpaid on Deposited Mail Matter That’s why a business can’t stuff flyers directly into your mailbox and why a neighbor technically shouldn’t drop a note inside either.16U.S. Government Accountability Office. U.S. Postal Service Information About Restrictions on Mailbox Access
Cluster Box Units for Multi-Unit Housing
New residential developments, apartments, and HOA communities typically use centralized cluster box units instead of individual curbside boxes. Individual compartments must fall between 28 and 67 inches above ground, with at least one compartment no higher than 48 inches to meet ADA accessibility. Units must be within walking distance of the residences they serve, ideally with canopy coverage and lighting. Site plans and equipment need approval from the local USPS Growth Manager before installation, and the property owner — not USPS — handles ongoing maintenance.
Mail Theft Is a Federal Crime
Taking mail from a mailbox, postal carrier, or post office, or receiving stolen mail knowing it was taken, carries up to five years in federal prison under 18 U.S.C. 1708.17Office of the Law Revision Counsel. 18 U.S. Code 1708 – Theft or Receipt of Stolen Mail Matter Generally The law applies equally to someone raiding a cluster box, swiping a package off a porch after USPS delivery, or intercepting mail at any point along the way.
Report mail theft to the U.S. Postal Inspection Service, which investigates it as a federal matter, rather than to local police. Informed Delivery, a free USPS service that emails scanned images of incoming letter mail each morning, won’t stop a thief but gives you a record that something was sent and a head start on reporting a loss.
Filing a Claim for Lost or Damaged Mail
If an insured package is lost or arrives damaged, you can file an indemnity claim with USPS, and the timing depends on the service. For Priority Mail, USPS Ground Advantage, insured mail, and COD, you can file after 15 days from mailing and must file within 60 days. Priority Mail Express has a shorter 7-day wait. For damaged items or missing contents, you can file immediately but the same 60-day outer deadline applies.18United States Postal Service. File a USPS Claim: Domestic Military addresses (APO/FPO/DPO) get significantly longer, up to one year depending on the service.
Maximum insurance coverage for standard domestic shipments is $5,000.19USPS.com. Insurance and Extra Services To collect, you’ll need proof you purchased the service (your mailing receipt or online label record) and proof of the item’s value, such as a sales receipt, invoice, or statement from a reputable dealer. Without both, the claim stalls.20Postal Explorer. 609 Filing Indemnity Claims for Loss or Damage Submitting only the outer packaging without a mailing receipt can cap your indemnity at $100 or less depending on the service. Keep receipts until delivery is confirmed.
International Shipments and Customs
Almost every item leaving the country needs a customs declaration listing what’s in the package, what each item is worth, and what it’s made of.21United States Postal Service. U.S. Customs Forms The main exception is First-Class Mail International letters and large envelopes under 15.994 ounces. Vague or inaccurate descriptions risk having the package held, returned, or seized on the receiving end.
You can complete customs forms at a post office retail window or through USPS online tools that print the shipping label and declaration as a single document. The form itself warns that a false or misleading declaration can trigger fines, seizure, and criminal or civil penalties.22United States Postal Service. PS Form 2976-R – Customs Declaration and Dispatch Note Check the destination country’s own restrictions before shipping. Many countries limit food, medications, and electronics that move domestically without a second thought. Once the package leaves the U.S. network, tracking updates get thinner and sometimes stop, and the destination country can assess duties or taxes that the recipient must pay before taking delivery.
Changing Your Address
Filing a change of address with USPS redirects your First-Class Mail and packages to your new address. You can file PS Form 3575 online or in person at any post office with valid ID, and the request won’t activate until your identity is verified.23USPS.com. What Does PS Form 3575 Mail Forwarding Change of Address Order Look Like First-Class Mail forwarding lasts 12 months for a permanent move, and periodicals forward for 60 days. After that, unforwarded mail goes back to the sender.
One boundary worth knowing: a USPS change of address does not update your voter registration. If you’re filing a permanent move, update your registration separately through your state’s election office.