Server 2012R2 DNS server returning SERVFAIL for some AAAA queries

I've looked into the network tace some more and done some reading. The reqest for the AAAA record, when non-existant, returns an SOA. Turns out the SOA is for a different domain that that being requested. I suspect that's why Windows is rejecting the response. Request AAAA for mx.atomwide.com. Response SOA for lgfl.org.uk. I will see if we can make some progress with this information. EDIT: Just for future reference, temporarily turning off "Secure cache against pollution" will allow the query to succeed. Not ideal, but proves the issue is with a dodgy DNS record. RFC4074 is also a good referemce - Intro and Section.