If you work in the ISP space you might need to check if a down or upstream server is set up to allow Zone Transfers (AXFR).

Test via:

dig -b your-dns-server-ip-with-permission-address @their-dns-server-ip-address exampleDomain.com AXFR
eg. dig -b 8.8.8.8 @208.67.222.222 exampleDomain.com AXFR

And it should return some records about the zone!