[exim] Spam from domain yahoo.com

I use callout verify, spf verify and all other methods, but the domain yahoo.com
is 95% of received SPAM.

Have a Mysql or other method to block email from yahoo.com only in "mx of
yahoo.com"??? How to contact the administrator of yahoo.com to set a TXT of spf
to yahoo.com???

Thanks from City of Iguassu Falls, Brazil
Silmar A. Marca