This means that mail from a friendly site might be blocked just because the administrator at that site misconfigured relaying. Using a blackhole list service is simple but inflexible because you can't choose which sites are listed. dnl Point dnsbl to our local DNS blackhole list FEATURE(`dnsbl', `')įollowing Recipe 1.8, rebuild the sendmail.cf file, copy the new sendmail.cf file to /etc/mail, and restart sendmail. Alternatively, the enhdnsbl feature can be used. Identify the local DNS blackhole list on the dnsbl command line. On the sendmail system, create a configuration containing the dnsbl feature. This is normally done by creating a special subdomain for the blackhole list within the zone of authority of the DNS server. The DNS server must be authoritative for the domain in which the blackhole list is to be located.

This format means that hosts are blacklisted by IP address instead of by name, which makes sense because the dnsbl lookup is done using the connection IP address. The special DNS address records in the zone file are constructed by reversing the IP address of the blacklisted system to create the DNS name field of the record and by using an address such as 127.0.0.2 in the data field of the address record. The domain administrator must create a DNS zone file, in the proper format, that lists all of the connection addresses that are to be blacklisted. You need to create your own DNS blackhole list because no external blackhole service provides exactly the listing policy and content you need.

Dns blackhole