What customs may do with a parcel in the mail

The default is that everything is examinable

The rule is written as a general statement with named exceptions. All mail arriving from outside the customs territory of the United States that is to be delivered within it is subject to customs examination.

Three categories fall outside. Mail known or believed to contain only official documents addressed to officials of the federal government. Mail addressed to ambassadors and ministers of foreign countries. And letter class mail known or believed to contain only correspondence or documents addressed to diplomatic missions, consular posts, or designated international organizations.

Those exceptions describe senders and recipients, not contents. Nothing in the list turns on what a parcel holds or how it was declared.

A separate provision covers diplomatic pouches. Mail articles bearing the official seal of a foreign government, with certificates stating they contain only official communications or documents, are admitted free of duty without customs examination.

The part also opens with a warning about its own scope. It says it does not contain all the regulations applicable to mail importations. Importations by mail are subject to the same requirements and restrictions as importations by any other means, except where the part sets out something more specific.

The line the rules actually draw is around correspondence

Sealed letter class mail gets a specific protection, and it is narrower than it is usually assumed to be.

Take the case of sealed letter class mail that appears to contain matter in addition to, or other than, correspondence. Customs officers may open and examine it, provided they have reasonable cause to suspect the presence of merchandise or contraband.

Where it appears to contain only correspondence, the standard changes. It may not be opened unless a search warrant has been obtained from an appropriate judge or United States magistrate, or unless the sender or the addressee has given written authorization.

Reading is treated separately from opening. No customs officer may read, or authorize anyone else to read, correspondence contained in any letter class mail, sealed or not, without a warrant or the written authorization of the sender or addressee.

The practical shape of that is worth stating plainly. The warrant requirement attaches to letters. A package that appears to hold goods is examined on a suspicion standard, not a judicial one.

Seizure, detention and the notice that follows

The seizure provision in the mail rules is short. All mail shipments containing articles whose importation is prohibited, or articles imported in any manner contrary to law, are seized or detained as appropriate and held by customs officers for appropriate treatment.

A notification duty is attached to it. In all cases where articles are seized or detained, the addressee is to be notified of the seizure or detention, of the reason for it, and, if appropriate, of the right to petition for relief.

That right runs through the fines and penalties rules. Either the addressee or the sender may file a petition with the Fines, Penalties, and Forfeitures Officer having jurisdiction over the port, asking for relief from the forfeiture and for release of the seized merchandise.

A small number of categories are handled by the postal service instead of by customs, including lottery matter. Obscene matter and several other categories named in section 305 of the Tariff Act are given customs treatment.

That section lists five types of prohibited article. Obscene matter. Articles for causing unlawful abortion. Matter advocating treason or insurrection against the United States, or forcible resistance to any law of the United States. Matter containing a threat to take a life or inflict bodily harm on any person in the United States. And lottery matter, with a narrow exception.

Two neighboring sections point outward rather than deciding anything. One states that certain plants, food, drugs, cosmetics, hazardous substances, viruses, serums and various harmful articles are subject to examination and clearance by the appropriate agencies before release to the addressee. The other says that further restrictions on particular kinds of merchandise apply to importations by mail as they do to anything else.

A third names a detention that is not a seizure. Merchandise subject to the Treasury sanctions rules is detained until it is licensed, or until the question of its release, seizure or other disposition has been determined under those rules.

The parcel that is never delivered

A mail article can fail to arrive without ever being seized, and the rules say where it goes.

Articles that are refused or undeliverable are marked by the postmaster to show why delivery was not made, and forwarded to the proper exchange post office for return to the country of origin. Any mail entry is removed and returned to customs for cancellation.

Suppose an undeliverable article known or supposed to be dutiable is neither returned to the country of origin nor forwarded elsewhere. It is then delivered to customs, for disposition under the laws governing seized or unclaimed merchandise.

Marking is one route into that outcome. Merchandise imported by mail has to be marked with the country of origin under the marking rules, and where the addressee fails to comply, the article is treated as undeliverable.

Duty-free status is another. Where a shipment is claimed as conditionally free, the port director may hold it while proof is requested from the addressee. If the proof does not arrive within thirty days, a mail entry is issued at the ordinary rate of duty and forwarded with the shipment for collection.

Disagreeing about the duty charged

The mail rules include a review procedure that most people never use, and it has clocks on it.

An addressee who thinks the duty assessed is wrong has more than one route. Duty can be paid and delivery taken, with a copy of the mail entry and a statement of the reasons sent to the issuing office along with any invoices or bills of sale. Acceptance can instead be postponed, with a written statement of objections given to the postmaster, who forwards it with the entry to the port director and keeps the shipment until instructed.

A formal protest is the third route. For mail entries made after the middle of December 2004, a protest has to be filed no later than one hundred and eighty days after the addressee pays the duties.

If the port director is satisfied the objection is valid and timely, the entry is amended and a refund issued. If not, the addressee gets written notice that the request was denied.

One line at the end of that subpart is easy to miss. Rates of duty assessed on a mail entry, whether on the original entry or on an amendment, are not binding for future importations.

A binding answer has to be obtained a different way. The regulation points to the procedures for requesting a ruling on tariff classification, which is a separate process with its own part of the rules.

There is also a route out of the country that runs the other way. Merchandise imported into the United States, unless it is nonmailable, may be exported by mail without payment of duties. Two conditions apply: it has to have remained continuously in government custody, and the articles have to be inspected and mailed under customs supervision. A waiver of the right to withdraw the article from the mails is endorsed on each package and signed by the exporter.

Sources

Each document below is named as it names itself, with the date printed on that document rather than the day it was read.

1. 19 CFR 145.2 and 145.3 — Mail subject to customs examination, and opening of letter class mail with the prohibition on reading correspondence — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
2. 19 CFR 145.59 and 145.4 — Seizures, the notification duty owed to the addressee, and the petition for relief from forfeiture — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
3. 19 CFR 145.5, 145.14 and 145.42 — Undeliverable packages, marking requirements and the failure-to-mark consequence, and proof for conditionally free merchandise — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
4. 19 CFR 145.21 through 145.26 — Administrative review of mail entries, the protest deadlines, amendment of entry, and the rule that assessed rates are not binding for future importations — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
5. 19 CFR 171.1 and 171.2 — Petition for relief, its required contents, and the thirty-day filing window for seizures — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026