Inform the sender by other means if you can, that they may have a mail virus/worm or some mass mail prog, that keeps sending you the message repeatedly, then set up a temporary spam filter with outlook to block receipt from that source, not ideal, but it worked for me when this last happened
A POINT OF NOTE :
When this last did happen, the sender (a major national competitor of mine) included their entire client base email addresses in the To: box ....
hehe