On Sun, Dec 07 2008, Sven Joachim wrote:

> On 2008-12-07 06:50 +0100, Lars Magne Ingebrigtsen wrote:
>> When the same message comes from two mailing lists, and there's not
>> enough information in them to identify them as such (to crosspost the
>> message between the list), the Message-ID has to be renamed.  Remove the
>> bit after __ to find the original ID.
>
> Here is some Emacs lisp code that does this automatically when replying
> in Gnus:
>
> (defun sj-unmangle-gmane-message-id ()
>   "Undo the Message-ID mangling that Gmane does on some postings."
>   (save-excursion
>     (save-restriction
>       (message-narrow-to-headers)
>       (goto-char (point-min))
>       (while
> 	  (re-search-forward "\\(<.*\\)" (point-max) t)
> 	(replace-match "\\1")))))

I would have expected a search for an expression like
"__[0-9.]+\\$gmane\\$org@" or similar.  What am I missing?

> ;; Fix up References header
> (add-hook 'message-header-setup-hook
> 	  'sj-unmangle-gmane-message-id)
>
> ;; Fix up In-Reply-To header
> (add-hook 'message-send-mail-hook
> 	  'sj-unmangle-gmane-message-id)
>
> Note that your own Gcc'ed copy will still have the mangled Message-ID in
> the In-Reply-To header, because message.el inserts that very late.  I
> can live with that, but if somebody has a better idea, please let me
> know.

I'd guess the unmangling should be done when `message-id' (fixing
References should not be necessary, I think) is put into
`message-reply-headers' (in `message-cite-original-1',
`message-reply', `message-followup'?).

Here's a very rough, untested patch: