What are the standard headers in NNTP?

Question

After looking at the NNTP standard, I have figured out how to extract a header from the message, how to fold headers, and how to separate the header label from the header text. What I can't find is an official list of standard NNTP headers. The standard lists Subject, From, Date, Message-id, Reference but not Groups which I know needs to be there.

Is there an official list of all the official NNTP headers? For bonus marks, is there a list of commonly-used, unofficial headers?

EDIT

I found the list of standard headers. Is there a similar list of non-standard, but common, headers?

Answer 1

You are not looking at the correct RFC the one you link to is the general message format.

Netnews is explicitly addressed in the Netnews Article Format RFC 5536 which lists the headers (with the page numbers of the RFC where they are defined) as

      3.1. Mandatory Header Fields ...................................10
           3.1.1. Date ...............................................11
           3.1.2. From ...............................................11
           3.1.3. Message-ID .........................................11
           3.1.4. Newsgroups .........................................13
           3.1.5. Path ...............................................14
           3.1.6. Subject ............................................16
      3.2. Optional Header Fields ....................................16
           3.2.1. Approved ...........................................17
           3.2.2. Archive ............................................17
           3.2.3. Control ............................................17
           3.2.4. Distribution .......................................18
           3.2.5. Expires ............................................19
           3.2.6. Followup-To ........................................19
           3.2.7. Injection-Date .....................................20
           3.2.8. Injection-Info .....................................20
           3.2.9. Organization .......................................22
           3.2.10. References ........................................22
           3.2.11. Summary ...........................................23
           3.2.12. Supersedes ........................................23
           3.2.13. User-Agent ........................................23
           3.2.14. Xref ..............................................24
      3.3. Obsolete Header Fields ....................................25
           3.3.1. Lines ..............................................25