DNS/KnotResolver/behavior/nxdomainについて、ここに記述してください。

$ dig qqqqqq.qmail.jp 

; <<>> DiG 9.11.1 <<>> qqqqqq.qmail.jp
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 40350
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 6f4580205537f7c46d50d4785909e555e0d7a23cde60cfb3 (good)
;; QUESTION SECTION:
;qqqqqq.qmail.jp.               IN      A

;; AUTHORITY SECTION:
qmail.jp.               2560    IN      SOA     a.ns.qmail.jp. hostmaster.m.qmail.jp. 1493567262 16384 2048 1048576 2560

;; Query time: 12 msec
;; SERVER: 127.0.0.3#53(127.0.0.3)
;; WHEN: Wed May 03 23:12:37 JST 2017
;; MSG SIZE  rcvd: 126

tmaeno@tm:~$ dig qqqqqq.qmail.jp 

; <<>> DiG 9.11.1 <<>> qqqqqq.qmail.jp
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 58530
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: e1d2e1338c513ada956c89b65909e56916cb3123628d7773 (good)
;; QUESTION SECTION:
;qqqqqq.qmail.jp.               IN      A

;; AUTHORITY SECTION:
qmail.jp.               2540    IN      SOA     a.ns.qmail.jp. hostmaster.m.qmail.jp. 1493567262 16384 2048 1048576 2560

;; Query time: 0 msec
;; SERVER: 127.0.0.3#53(127.0.0.3)
;; WHEN: Wed May 03 23:12:57 JST 2017
;; MSG SIZE  rcvd: 126

@400000005909e55f04c66b74 [    0][plan] plan 'qqqqqq.qmail.jp.' type 'A'
@400000005909e55f04c6fbfc [29049][iter]   'qqqqqq.qmail.jp.' type 'A' id was assigned, parent id 0
@400000005909e55f04c80d6c [29049][resl]   NT check; qqqqqqqmailjp cut qmailjp
@400000005909e55f04c81154 [29049][resl]   kr peekpkt qqqqqqqmailjp ret -2
@400000005909e55f04c8153c [15852][iter]   'qqqqqq.qmail.jp.' type 'A' id was assigned, parent id 0
@400000005909e55f04c81924 [15852][resl]   => querying: '14.192.44.5' score: 11 zone cut: 'qmail.jp.' m12n: 'QQqQqq.QMail.jp.' type: 'A' proto: 'udp'
@400000005909e55f057ef1bc [15852][iter]   <= rcode: NXDOMAIN
@400000005909e55f057fb124 [15852][ pc ]   => answer cached for TTL=900
@400000005909e55f057fd064 [15852][resl]   <= server: '14.192.44.5' rtt: 12 ms
@400000005909e55f058041ac [    0][resl] finished: 4, queries: 1, mempool: 32800 B
@400000005909e5732526f2bc [    0][plan] plan 'qqqqqq.qmail.jp.' type 'A'
@400000005909e5732527872c [63459][iter]   'qqqqqq.qmail.jp.' type 'A' id was assigned, parent id 0
@400000005909e5732527aa54 [63459][ pc ]   => satisfied from pktcache
@400000005909e5732527aa54 [63459][iter]   <= rcode: NXDOMAIN
@400000005909e5732528e6bc [    0][resl] finished: 4, queries: 1, mempool: 32800 B