blocking spam with sendmail

Can block by domain or by IP address or network

in /etc/mail/access:

localhost.localdomain RELAY
localhost RELAY
127.0.0.1 RELAY
192.168.1 RELAY
202.124.241.222 ERROR:"550 Take a hike"

As this is a hash, rebuild to db with:

hash /etc/mail/access < /etc/mail/access