RFC 2822 specifies the following groups of email headers:
The originator fields indicate the mailbox or mailboxes of the source of the message.
The destination fields indicate the intended recipients of the message.
Identification fields identify a message and the thread of replies.
The informational fields contain information about the message. They are optional, and intended to have only human-readable content.
Resent fields are added to identify a message reintroduced by a user into the transport system.
Resent fields are added for informational purposes to identify the one who resent the message and the time resent; the original fields should remain unchanged. The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function just like the "To:", "Cc:", and "Bcc:" fields, except for the fact that they indicate the recipients of the resent message, not the recipients of the original message.
For a full discussion of the use of trace fields, see RFC 2821.
Optional fields are fields that may appear in messages but that which are unspecified in RFC 2822. The field names of any optional-field must not be identical to any field name specified in that standard.
These nations are associated with the United States under a Compact of Free Association. They enjoy international sovereignty and ultimate control of their territory, but the United States provide defense, funding grants, and social services.
These are territories under the jurisdition of the United States.
"Incorporation" brings a territory permanently under the jurisdition of the Constitution of the United States -- once incorporated, an incorporated territory can no longer be de-incorporated. The U.S. Constitution is applied to the territory's inhabitants in its entirety (e.g., citizenship, trial by jury).
For unincorporated territories under U.S. jurisdiction, only certain "natural" protections of the Constitution apply (e.g., freedom of speech, due process), plus other parts the Congress has added.
The U.S. recognizes the inherent authority of indigenous tribes to govern themselves. Thus, Indian tribes are sovereign nations under U.S. law (their legal authority to exist derives independently of the state and federal governments). They are immune from regulations under state law, but they cannot act independently of the federal government. The political and economic rights of tribal governments are still regulated by Federal law, and all Indian land is held in trust by the United States.
In Cherokee Nation v. Georgia (1831), Chief Justice Marshall characterized the tribes as "domestic dependent nations," stating that "an Indian tribe or nation within the United States is not a foreign state in the sense of the constitution," but that these domestic nations "are in a state of pupilage" and that "their relations to the US resemble that of a ward to his guardian."
Although Congress extended national citizenship to members of enrolled tribes in 1924, a court decision held that "the granting of citizenship did not destroy ... jurisdition of tribal courts." A previous case law said that "when Indians are prepared to exercise the privileges and bear the burdens of one sui juris (not under the power of another), the tribal relation may be dissolved and the national guardianship brought to an end, but it rests with Congress to determine when and how this shall be done, and whether the emancipation shall be complete or only partial ..." (U.S. v. Nice, 1916).
The courts also have determined that "It is thoroughly established that Congress has plenary authority over Indians." and that no law had ever extended provisions of the US constitution, including the right of habeas corpus, to tribal members brought before tribal courts.
Therefore, Indian courts should be seen, at least in part, as arms of the federal government, because "originally they were created by federal executive and imposed upon the Indian community, and to this day the federal government still maintains a partial control over them," even though "it does not follow from our decision that the tribal court must comply with every constitutional restriction that is applicable to federal or state courts" (U.S. Court of Appeals, Ninth Circuit, 1965).
Source: Tribal sovereignty