Some USPS packages are X-rayed, but not all of them, and there is no published rule that says which ones will be. Mail moving through large processing centers has the highest chance of being scanned, and X-ray is only one of several screening tools the Postal Service uses to keep dangerous and illegal items out of the mail stream.
How USPS Screens the Mail
X-ray machines let postal inspectors see the shapes and densities inside a package without opening it. Large mail processing centers are the most common places this happens, so a package routed through a major hub is more likely to be scanned than one that stays local. Writing “Do Not X-Ray” on the outside will not stop screening and can cause the package to be treated as suspicious.1USPS. Mail Security
X-ray is one layer. Postal inspectors also use portable X-ray equipment, biological detection systems that alert on dangerous biological agents, and trace detection tools that pick up microscopic explosive or narcotic residue on a package’s surface. Trained detection dogs work at postal facilities, and postal workers do visual inspections looking for unusual odors, leaking liquids, excessive postage, and other red flags.
Screening a Package Is Not the Same as Opening It
USPS can run any package through an X-ray without a warrant. Whether a postal worker can actually open your mail depends on how you shipped it.
Federal law requires USPS to keep at least one class of mail “sealed against inspection,” which means it cannot be opened without a federal search warrant, the addressee’s consent, or a narrow exception for determining a delivery address.2Office of the Law Revision Counsel. 39 USC 404 – Specific Powers Several classes carry this protection:
- First-Class Mail
- Priority Mail
- Priority Mail Express
- USPS Ground Advantage (Retail and Commercial)
USPS employees generally cannot open these to check contents or verify postage.3USPS. Can My Mail Be Opened? Unsealed classes get less privacy protection. Periodicals, USPS Marketing Mail, Package Services, Media Mail, and Library Mail can all be opened by postal employees to verify proper postage or confirm the contents are mailable.4eCFR. 39 CFR 233.3 – Mail Covers Sending something at Periodicals rates is treated as consent to inspection.
When Sealed Mail Can Be Opened Without a Warrant
There are real exceptions to the warrant rule. Aviation safety is the biggest. Mail heavy enough to pose a hazard aboard an aircraft can be screened by any means necessary to identify explosives, firearms, or other dangerous contents, and no warrant or sender consent is required.5eCFR. 39 CFR 233.11 – Mail Screening
For mail going by ground, the bar is higher. Warrantless screening requires either exigent circumstances or a determination by the Chief Postal Inspector that a credible threat exists, such as intelligence suggesting a piece of mail may contain a bomb or material that could endanger lives.5eCFR. 39 CFR 233.11 – Mail Screening If screening raises doubts about a sealed package that cannot be resolved without opening it, the item gets reported to the Postal Inspection Service for further instructions rather than opened on the spot.
A separate rule covers mail that screening flags as an immediate danger to life or property. Sealed or not, that piece can be detained, opened, and neutralized without a warrant, but only to the extent needed to identify and eliminate the threat.
What You Cannot Send Through the Mail
Some items are prohibited outright and cannot be mailed under any circumstances: explosives and ammunition, gasoline, liquid mercury, and marijuana (including medical marijuana, regardless of state law).6USPS. Shipping Restrictions and HAZMAT – What Can You Send in the Mail?
Others are restricted, meaning they are mailable only if you follow specific packaging, labeling, and declaration rules. Mailable gases and aerosols like propane, butane, and fire extinguishers can be shipped with proper handling. Small consumer lithium batteries (the kind in cameras and flashlights) are allowed in domestic mail under specific conditions. Only licensed manufacturers and dealers can mail handguns; unloaded rifles and shotguns are mailable by individuals under strict rules. Beer, wine, and liquor generally cannot go through the mail except in limited circumstances. Getting the details wrong on a restricted item can trigger the same penalties as shipping a prohibited one.
Hemp-derived products, including CBD, can be mailed domestically if THC content is 0.3 percent or less, following USPS Publication 52, Section 453, with lab test results and licenses kept for at least two years. Hemp and CBD cannot be sent to international or military destinations.
Penalties If a Prohibited Item Is Found
Knowingly mailing anything declared nonmailable, including poisons, explosives, and other injurious articles, carries up to one year in federal prison, a fine, or both. If the act is done with intent to kill, injure, or damage property, the maximum jumps to 20 years. If someone dies as a result, the penalty can reach life imprisonment or the death penalty.7Office of the Law Revision Counsel. 18 USC 1716 – Injurious Articles as Nonmailable Mailing controlled substances is prosecuted under federal drug distribution statutes regardless of state legalization, because USPS is a federal system.
Civil penalties run separately from any criminal case. A person who knowingly mails hazardous material in violation of postal regulations faces civil penalties between $250 and $100,000 per violation, plus cleanup costs and damages. Each item counts as a separate violation, and each day the material stays in the mail stream adds another. You do not need to know a specific regulation exists to be liable; if a reasonable person in the same circumstances would have known the material was hazardous or restricted, that meets the “knowing” standard.8Office of the Law Revision Counsel. 39 USC 3018 – Hazardous Material
What Happens to a Flagged Package
A package pulled during screening is isolated and secured, and postal inspectors are notified. Immediate physical threats are handled by specialized hazardous materials teams.
For suspected illegal drugs, the Postal Inspection Service usually runs an administrative process before seeking a search warrant. Inspectors request consent from the sender or addressee to open the detained package. If no one responds within 21 days, the package is declared abandoned and inspectors can open it without a warrant. Nonmailable contents are seized and disposed of, while mailable items found alongside them are returned to the addressee.9USPS Office of Inspector General. U.S. Postal Inspection Service Handling of Suspected Marijuana Packages
To challenge a forfeiture, you must file a written claim that identifies the specific property, states your interest, and is sworn under penalty of perjury. The deadline depends on how you were notified: at least 35 days from the date personal written notice was sent, or at least 30 days after final publication of a seizure notice if you were not personally notified. The claim must reach the specific official named in the notice; filing with the wrong office does not count.10eCFR. 39 CFR 233.7 – Forfeiture Authority and Procedures
If You Are Shipping Something X-Ray Sensitive
Unprocessed photographic film is the main consumer item genuinely at risk. High-intensity scanners, especially the type used for checked airline baggage and air freight, will fog and ruin unprocessed film of any speed. The safer option is ground shipping, and telling the carrier the shipment contains unprocessed film that should not be X-rayed.11Kodak. Transporting and Storing Film Standard consumer electronics are not harmed by the X-ray energy levels used in postal screening. Writing “Do Not X-Ray” on a package will not prevent screening and may draw extra attention; choosing USPS Ground Advantage or another surface-only service avoids aviation-level screening in the first place.