DNSBL Check
This tool allows you to check the blocklist status of your mail server's IP address.
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Host | Listed? |
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About this tool
This tool checks the blocklist status of your mail server's IP address. You can either lookup up with an IPv4 or IPv4 address or hostname.
DNSBL
Domain Name System Blocklists, also known as DNSBL's or DNS Blocklists, are spam blocking lists that allow a website administrator to block messages from specific systems that have a history of sending spam. As their name implies, the lists are based on the Internet's Domain Name System (DNS).
When a mail server receives a connection from a client and wishes to check that client against a DNSBL (let's say, dnsbl.example.com), it does more or less the following:
- Take the client's IP address—say, 78.46.19.133—and reverse the order of octets, yielding 133.19.46.78.
- Append the DNSBL's domain name: 133.19.46.78.dnsbl.example.com.
- Look up this name in the DNS as a domain name ("A" record). That will return either an address indicating that the client is listed or an "NXDOMAIN" ("No such domain") code, indicating that the client is not.
- Optionally, if the client is listed, look up the name as a text record ("TXT" record). Most DNSBLs publish information about why a client is listed as TXT records.