Domain Name System Blacklists, also known as DNSBL's or DNS Blacklists, are spam blocking lists that allow a website administrator to block messages from specific systems that have a history of sending spam.
To enable external DSN based blacklist feature on your sendmail server, you can add the below mentioned configuration in the sendmail.mc file located in /etc/mail . Below I have mentioned eight dnsbl configurations, You can choose the black list based on your environment, server load etc and add it .
Edit sendmail.mc
#vim /etc/mail/sendmail.mc
FEATURE(`enhdnsbl', `bl.spamcop.net', `"Spam blocked see: http://spamcop.net/bl.shtml?"$&{client_addr}', `t')
FEATURE(dnsbl,`combined.njabl.org',`Message from $&{client_addr} rejected - see http://njabl.org/lookup?$&{client_addr}')
FEATURE(rhsbl,`dsn.rfc-ignorant.org',`"550 Mail from domain " $`'&{RHS} " refused. MX of domain do not accept bounces. This violates RFC 821/2505/2821 - see http://www.rfc-ignorant.org/"')
FEATURE(`dnsbl', `zen.spamhaus.org', `"Rejected due to Spamhaus listing see http://www.abuse.net/sbl.phtml?IP=" $&{clientaddr} " for more information"')
Restart the sendmail service
#service sendmail restart
External Links:
www.dnsbl.info
www.spamcop.net
