Occassionally I am seeing an Authority SOA answer response to an MX query, instead of returning the normal mail server answer. What is the significance of it? The requests look identical, but sometimes the Authority SOA answer is returned. The domain is valid and the MX records for that domain are present in the DNS server.

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Query Id: 463
Flags: 1000 0101 1000 0000
Number of Question RRs: 1
Question 1: xyz.state.zz.us MX (9500) IN (9507)
Number of Answer RRs: 0
Number of Authority RRs: 1
Authority 1: xyz.state.zz.us 3600 SOA (9491) IN (9507) nameserver1.xyz.state.zz.us
hostmaster.xyz.state.zz.us ( 2006467839 900 600 86400 3600
Number of Additional RRs: 0
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