USENET features several newsgroup types. The type affects the security mode of a newsgroup, controlling who can post and how posts are secured.
In current systems, this type is stored as a one-character flag in the newsgroup database known as the "active" file in most systems and under the NNTP standard. Arguments to the "newgroup" control message and related messages set and change such flags.
The following newsgroup types are defined, along with the arguments to a newgroup message. To remain compatible with old software, certain new types of group are definited initially as moderated.
A traditional unmoderated group. Any party may post.
A traditional moderated group. All postings MUST be signed by a party with a certificate enabling posting in this group. Typically this party is the "moderator" who takes postings from others, signs them and posts themto the group. In addition, for bacwkards compatibilty, all postings MUST contain an "Approved" header containing an E-mail address associated with the moderator.
Postings without proper authentication SHOULD be forwarded to the moderator, whose address is available in other databases. As a default, a moderator's address may be formed by taking the newsgroup name, replacing dots with dashes to form a userid, and mailing to that userid at the Internet domain "moderators.usenet.com"
As a moderated group, except postings from regular users are not welcome, and MUST NOT be forwarded by E-mail. All postings MUST contain both a signatre with certificate enabling posting to the group, and an Approved header.
Not actually a moderated group. Postings may be made by any party, but MUST be signed. The signing party MUST have a certificate certifying any E-mail addresses used in the From:, Reply-to:, Sender: or Approved: header, however the certificate need not certify posting in the particular group.
Postings without such authentication MAY be rejected to the user with an error at posting time, and otherwise SHOULD be forwarded to the moderator address, if present.
Two additional flags can be present on newgroup messages. They apply to all states, with exceptions as noted.
This newsgroup actually has no moderator address to which one can forward unauthorized postings. If possible, the user attempting to post an unauthorized posting SHOULD be given an error message. If not, the message should be discarded. This is the default for a "noposting" group, and in effect a noposting group is a moderated group with the "-moderator" flag.
This flag is most commonly set on "unmoderated" groups, where the default is that regular named articles need no certificate or signature. It also can be applied to other groups (such as "moderated +authenticated" groups) to indicate that a regular posting certificate within the group is sufficient to post unsecured named articles.
Secured named articles (those whose names begin with "_") always require a certificate enabling the posting of the particular article in the particular group to be accepted.
The above complex syntax is present to remain compatible with older software. In essence there are really the following 4 status bits on a group: