Blacklist in detail:

The Measurement Factory: Open Resolvers IPv4

This is not an actual SPAM DNSBL. This list contains IP's of open DNS resolvers. An open DNS resolver is a DNS that provides name resolution outside of its administrative domain.

According to the RBL website they check IP addresses by querying the IP's at most every three days.

Last Accessed
2020-07-11 07:35 (UTC) 
Last Checked
When we last checked 2 hours, 25 minutes ago it was working.
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History for (Last 10 Days)

We keep some statistics on blacklists. Below is the graph for We test blacklists by asking them to respond to known IP's that are blacklisted and known IP's that can't be blacklisted. Not every blacklist has such IP's, we test them with what is possible. We keep if we get any response or error messages and the response duration. Lower response times are better. These statistics may be useful for email server administrators to pick which blacklist to use.

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