Definition
As a legal adjective, postal means of or relating to the mails and the post office system. It is used primarily as a modifier to describe activities, regulations, offenses, services, or instruments that fall within the jurisdiction or operation of the government mail system.
The term does not define a legal doctrine on its own but anchors a cluster of legally significant concepts: postal fraud, postal inspectors, postal rates, and the constitutional framework under which Congress regulates the mails. In statutory and regulatory law, "postal" most often appears in compound terms rather than standing alone.
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Common Language
Modern common usage (Wiktionary): Relating to the collection, sorting, and delivery of mail. Colloquially also used to mean crazy or erratic, as in "going postal."
Historical common usage (Webster's 1913): Belonging to the post office or mail service; as, postal arrangements; postal authorities.
The legal meaning aligns closely with the common meaning, but researchers should note that in legal contexts "postal" carries jurisdictional and regulatory weight that the ordinary adjective does not. A "postal matter" in a federal statute is a term with defined scope; in ordinary speech it is merely descriptive. The slang meaning ("going postal") has no legal significance and should not create interpretive confusion in legal sources.
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Why It Matters in Research
Postal law is an area where federal preemption is near-total in U.S. sources. When researching any matter labeled "postal," researchers should expect to be working primarily in federal statutory and regulatory materials, not state law.
The term's most important legal uses are in compound forms. Researchers encountering "postal fraud" in older sources should be alert to the evolution of what is now the federal mail fraud statute — historically prosecuted under postal fraud theory, it expanded significantly in scope during the twentieth century. The connection between "postal" and federal criminal jurisdiction is one of the more consequential relationships in the corpus.
Postal currency is a historically bounded term appearing in post-Civil War American legal and financial sources. It describes a transitional instrument — Congress-authorized fractional paper notes used when coins were hoarded — and should not be confused with postage stamps, postal money orders, or any modern instrument. Researchers encountering this term in case law or legislative history from roughly 1862–1876 should treat it as a period-specific financial term, not a continuing legal category.
Postal money orders and postal notes are distinct instruments with different legal characteristics and different periods of use. Postal notes were discontinued in the United States in the 1890s. Researchers in late nineteenth-century commercial or probate materials may encounter them as assets in estates or as evidence of payment.
The overlap between postal law and constitutional law is significant for researchers working on the commerce clause, the necessary and proper clause, or First Amendment press and speech issues — Congress's postal power has been invoked both to protect and to suppress communications at various points in American legal history.
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Historical Dictionary Support
Both editions of Black's define postal simply as "relating to the mails; pertaining to the post office." The definitions are functionally identical and offer no doctrinal elaboration.
The second edition is more useful for historical research because it includes the postal currency entry, which provides both a definition and historical context for the Civil War-era instrument. Black's correctly identifies the scarcity of specie change as the driver of the practice and notes Congress's authorization, but does not address the legal disputes that arose over the status of these instruments or their redemption.
Webster's 1913 adds postal card and postal money order as illustrative compound terms, consistent with contemporary usage, and its treatment aligns with both Black's editions. None of the historical sources address postal inspectors, postal fraud, or the regulatory architecture that became the dominant legal significance of the term in the twentieth century — a gap researchers should keep in mind when working in pre-twentieth-century materials.
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Jurisdictional Note
In the United States, postal law is exclusively federal. The U.S. Postal Service operates under federal statute, and mail fraud jurisdiction rests in federal courts. Researchers working in Commonwealth jurisdictions (U.K., Canada, Australia) will encounter "postal" in analogous but separately structured regulatory frameworks and should not assume U.S. federal postal law applies.
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