[Exim] Long spaces in subject line

Hello.

I was hoping an expert user might be able to help me with a small
issue I'm having.

I would like to bounce any messages that contains more than 8
consecutive spaces in the message subject. (Not checking spaces
used to wrap the Subject header across multiple lines.)

I've set up a system filter, but I don't think it recognizes blank spaces.

#       $h_subject contains "        "

Any solution would be greatly appreciated.


George