I am currently running a bunch of tests on DNS resolver software called Unbound to see what it is worth and for that needed a list of valid domain names in different but controllable TLDs. The only resource to download such list I could find was 3 million records file from Nominum Sample query data file for use with resperf . Only that it contains all kinds of record types : A, PTR, AAAA and I want list of domain names where I can modify query type but also that it will be of a specific TLD sample.
Say all domains in .ASIA only TLD . To compile such list I took a word list , added to each word specific extensions and then run against some DNS server. Then I filtered the answers to include only existing resolvable domains that return at least 1 answer to query ANY. So far I did it for extensions : .ASIA .COM .CA .BIZ .EDU .EU .FR .INFO .MIL .NET .ORG .RU and it brought 831903 valid domains.
You can download the final list of those domains here : Domain list 831903 domains
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