DNSBL Monitor

This is an application whose sole intention is to check whether or not a set of given IPs or domains can currently be found on a set of given blacklists.

This was done to learn more about Erlang/Elixir and how blacklists work, and it's not really inteded for anyone to use it.

How it works

How to query DNSBL

For an IP address of 12.23.34.45:

1. Reverse order of octets: 12.23.34.45 -> 45.34.23.12
2. Append DNSBL URI: 45.34.23.12.zen.spamhaus.org
3. Query your recursive DNS for A record of this URI, which will either result in an address if the IP address is listed, or NXDOMAIN if it is not
4. For listed IPs query TXT record for the URI to find the explanatory message: https://www.spamhaus.org/sbl/query/SBL123456

For a domain of test.surbl.org:

1. Append the DNSBL URI: test.surbl.org.multi.surbl.org
2. Query your recursive DNS for A record of this URI, which will either resolve to an IP address if the address is listed, or NXDOMAIN if it is not
3. For listed addresses, query the TXT record for the URI to find the explanatory message: wild.surbl.org permanent test point

How to use it

If you do decide to use it:

• Create a file with one IPv4 address or domain per line
• Create a file with one blacklist address per line
• Run mix check <addresses-path> <blacklists-path>