The Message-ID line gives the message a unique identifier. The Message-ID may not be reused during the lifetime of any previous message with the same Message-ID. (It is recommended that no Message-ID be reused for at least two years.) Message-ID's have the syntax:

<string not containing blank or ">">

In order to conform to RFC-822, the Message-ID must have the format:

<unique@full_domain_name>

where full_domain_name is the full name of the host at which the message entered the network, including a domain that host is in, and unique is any string of printing ASCII characters, not including "<" (left angle bracket), ">" (right angle bracket), or "@" (at sign).

For example, the unique part could be an integer representing a sequence number for messages submitted to the network, or a short string derived from the date and time the message was created. For example, a valid Message-ID for a message submitted from host ucbvax in domain "Berkeley.EDU" would be "<4123@ucbvax.Berkeley.EDU>". Programmers are urged not to make assumptions about the content of Message-ID fields from other hosts, but to treat them as unknown character strings. It is not safe, for example, to assume that a Message-ID will be under 14 characters, that it is unique in the first 14 characters, nor that is does not contain a "/".

The angle brackets are considered part of the Message-ID. Thus, in references to the Message-ID, such as the ihave/sendme and cancel control messages, the angle brackets are included. White space characters (e.g., blank and tab) are not allowed in a Message-ID. Slashes ("/") are strongly discouraged. All characters between the angle brackets must be printing ASCII characters.

RFC1036: [Source:"RFC-1036"] [Last Changed:December 1987] [Copyright: 1987 M. Horton, R. Adams]
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(Corrections, notes, and links for Usenet RKT.)
by Mib Software, INN customization and consulting

For POSTing, modern newsreaders require only "From" "Subject" and "Newsgroups" and will generate the remaining lines. See the note: NNTP-Ext 4.2 The Required Headers in an Article and the POST command

-B-r-o-a-d-e-n- your knowledge

Up to RFC1036 2.1. Required Header lines