[Exim] helo verifying

Hi!

I wonder how I could filter specifically for hosts, pretending to be me,
i.e. send my IP address as helo address. I don't want to do the full
helo_verify as that seems to cut out some legitimate mail from badly
set-up ISP's, but if someone sends my IP address as helo, it seems
always to be spam. Can someone tell me how I could reject those? (exim 4.20)

thanks,

Marcus