[Exim] HELP stopping open relay

Hi,
I've come across this problem of my mail servers being able to deliver
any email in inverted commas at my domain eg:
"anyemailaddress@???

Would anyone have any idea on how I can close this open relay.....

Thanks,

Doug Bean          |  .''`.  ** Debian GNU/Linux **
Mr Bean's Internet | : :' :      The  universal
airliebeach.net.au | `. `'      Operating System
www.mrbean.net.au  |   `-    <http://www.debian.org/>