Ok, do you mean that this problem can not be fixed ? Or it could but
it would be hard to fix manually each broken message-ID ?

Lars Magne Ingebrigtsen <larsi at gnus.org> writes:

> Samir Saidani <saidani at squeakfr.org> writes:
>
>> It seems that this change is involved in the problem. Hope this
>> indication would help you to figure out what is the problem !
>
> It seems likely that the messages already were in a different group
> (or didn't have Message-IDs, or they were syntactically invalid), so
> the mail-to-news script assigned new Message-IDs.  Which breaks
> threading. 
>
> -- 
> (domestic pets only, the antidote for overdose, milk.)
>   larsi at gnus.org * Lars Magne Ingebrigtsen