I've sent it to Rick Moore a while ago, but dunno if it has been 
officially published as an FSC-xxxx...
==========================================================================
Document:   FSC-????
Date:       01-Oct-92


             Improving Fidonet/Usenet gating and Dupe Checking
                              
                      Franck Arnaud, Fidonet 2:320/100



 Status of this document
 -----------------------

This FSC suggests a proposed standard for the FidoNet(r) community,
and invites discussion and suggestions for improvements. Distribution of
this document is unlimited.

Fido and FidoNet are registered marks of Tom Jennings and Fido Software.
   

 Introduction
 ------------

The complexity of Usenet/Fidonet gating and the large number of gateways
has led to a non-negligible quantity of duplicates appearing regularly in 
both the Usenet and Fidonet worlds. This proposal defines a standard method 
for gateway software to deal with conversion of message identifiers between 
both worlds, so that we can improve the reliability of Usenet/Fidonet 
gateways.


 Fidonet to Usenet Message Identifiers Conversion
 ------------------------------------------------

The dupe checking in Usenet is based on the message ID. Fidonet now has its
own standard message identification standard (fts-0009).

So it would be interesting if the same Fidonet message gated at different
gateways had the same ID in Usenet to help news processing programs in
stopping dupes.

The proposed fido ^MSGID: to Rfc Message-ID: conversion method is defined
as below:

The Fidonet Message Identifier (the ^MSGID kludge)

    ^MSGID: z:n/f{.p}{@domain} 32-bit-hexdigit

is converted to the RFC822 Message_ID: header field:

    Message-ID: <z_n/f{_p}_lowered(32bithexdigit)@fidonet.org>


Some examples:

    (Fido) ^MSGID: 2:320/100 12345ABC
    becomes (Usenet) Message-ID: <2_320/100_12345abc@fidonet.org>

    (Fido) ^MSGID: 2:320/100.10@fidonet abcd6789
    becomes (Usenet) Message-ID: <2_320/100_10_abcd6789@fidonet.org>



 Usenet To Fidonet Message Identifier Conversion
 -----------------------------------------------

Another problem is preventing messages gated into Fidonet from RFC822 from
being gated back to Usenet at another gateway with a new message id. The
easy way to solve that is simply to store the RFC message ID in a kludge 
line. This kludge line could also allow identifying messages gated from 
Usenet (this could be used by message editors to allow private replies to 
the nearest uucp gateway for example).

It is proposed that the ^RFCID: kludge is used to store the RFC Message-ID:
in Fidonet messages. Of course, the use of the RFCID kludge doesn't replace
the standard fts-0009 Message-ID:.

    (example gated message starts with:)
    ^MSGID: 2:320/100.1 6789fedc
    ^RFCID: 92_feb_10_19192012901@prep.ai.mit.edu

Then if a gateway finds a RFCID line in a Fido message, it will use it in
the Usenet message ID, instead of converting the ^MSGID.