> >(7) When  a message is  sent to  two or more  lists on the  same server,
> >users subscribed to  more than one of the lists  should receive only one
> >copy of the message.
>
> I'm not sure that this is  desirable. For one thing, it isn't consistent:
> the results would depend  on whether the lists are on  the same server or
> not.  The subscriber  could have  a  filter to  log the  mail in  various
> folders based on  which list it comes  from, and in that case  one of the
> two folders  would be selected  randomly to  receive the message,  and it
> wouldn't be in  the others. Again, while this saves  disk space, it isn't
> very consistent. It isn't even consistent with news where, while there is
> only one copy of the message, it will be shown in both newsgroups. With a
> mail interface this will not be the case.
 
I'm subscribed to a lot more lists on our own server than any other and
there is a fair amount of cross posting, so it would help quite a bit
in a common case here.
 
With regard to the filtering, the headers should mention both lists.
Wouldn't that take care of it?