Warning with duplicata removal

It is quite common for procmail users to have something like that:

:0:.duplicate.lock
* ? formail -D 8192 $HOME/.duplicate.procmail-cache
/dev/null
        
> From my experience at a small ISP, which uses procmail as the local 
delivery agent and have a /etc/procmailrc to perform various duties such 
as duplicata removal, this is dangerous. Some software seem to send 
*always* the same Message-ID, like this one:
                        
<MAPI(_dot_)Id(_dot_)0016(_dot_)00666479202020203030303430303034(_at_)MAPI(_dot_)to(_dot_)RFC822>
 

I don't know what MAPI is, but I've seen the same behaviour with some 
versions of Microsoft products. I suggest, either to consider Microsoft 
mail elimination as a feature or to guard the recipe:

:0
* !^X-msmail
* !^Message-ID: *<MAPI(_dot_)*(_at_)MAPI(_dot_)to(_dot_)RFC822>
{
        :0:/var/tmp/.duplicate.lock
        * ? formail -D 8192 $HOME/.duplicate.procmail-cache
        /var/tmp/mail-duplicates
}