duke.edu DNS IPv6 does not work

Is there anyone from duke.edu on this list? I am having problems with IPv6 on one of their sub-delegations causing mail delays. Trying to go through the front door writes me off with "not our problem".

dm.duke.edu. 21600 IN NS nameserver1.mc.duke.edu.
dm.duke.edu. 21600 IN NS nameserver2.mc.duke.edu.
;; Received 135 bytes from 152.3.105.232#53(dns-auth-02.oit.duke.edu) in 76 ms

nameserver1.mc.duke.edu has address 152.16.1.4
nameserver1.mc.duke.edu has IPv6 address 2620:0:691:dc50::4

nameserver2.mc.duke.edu has address 152.16.1.12
nameserver2.mc.duke.edu has IPv6 address 2620:0:691:dc57::12

Works on IPv4:

; <<>> DiG 9.10.3-P4-Debian <<>> MX dm.duke.edu @152.16.1.4
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4622
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; OPT=15: 00 12 ("..")
;; QUESTION SECTION:
;dm.duke.edu. IN MX

;; ANSWER SECTION:
dm.duke.edu. 3600 IN MX 10 mx.oit.duke.edu.

;; AUTHORITY SECTION:
dm.duke.edu. 86400 IN NS nameserver1.mc.duke.edu.
dm.duke.edu. 86400 IN NS nameserver2.mc.duke.edu.

;; Query time: 77 msec
;; SERVER: 152.16.1.4#53(152.16.1.4)
;; WHEN: Thu Sep 19 06:37:13 PDT 2024
;; MSG SIZE rcvd: 140

; <<>> DiG 9.10.3-P4-Debian <<>> MX dm.duke.edu @152.16.1.12
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7136
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; OPT=15: 00 12 ("..")
;; QUESTION SECTION:
;dm.duke.edu. IN MX

;; ANSWER SECTION:
dm.duke.edu. 3600 IN MX 10 mx.oit.duke.edu.

;; AUTHORITY SECTION:
dm.duke.edu. 86400 IN NS nameserver2.mc.duke.edu.
dm.duke.edu. 86400 IN NS nameserver1.mc.duke.edu.

;; Query time: 76 msec
;; SERVER: 152.16.1.12#53(152.16.1.12)
;; WHEN: Thu Sep 19 09:57:48 PDT 2024
;; MSG SIZE rcvd: 140

Fails on IPv6:

; <<>> DiG 9.10.3-P4-Debian <<>> MX dm.duke.edu @2620:0:691:dc50::4
;; global options: +cmd
;; connection timed out; no servers could be reached

; <<>> DiG 9.10.3-P4-Debian <<>> MX dm.duke.edu @2620:0:691:dc57::12
;; global options: +cmd
;; connection timed out; no servers could be reached

~Seth

Looks like they have removed the IPv6 addresses.

% dig nameserver1.mc.duke.edu aaaa
;; BADCOOKIE, retrying.

; <<>> DiG 9.21.0-dev <<>> nameserver1.mc.duke.edu aaaa
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51760
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: c31ab4004b3f1bf30100000066ecc7400b8f7da8be92918a (good)
;; QUESTION SECTION:
;nameserver1.mc.duke.edu. IN AAAA

;; AUTHORITY SECTION:
mc.duke.edu. 3290 IN SOA nc1-bc-hm1.dhe.duke.edu. hostmaster.dhe.duke.edu. 635464169 1200 180 1209600 3600

;; Query time: 0 msec
;; SERVER: ::1#53(::1) (UDP)
;; WHEN: Fri Sep 20 10:52:16 AEST 2024
;; MSG SIZE rcvd: 142

% dig nameserver2.mc.duke.edu aaaa
;; BADCOOKIE, retrying.

; <<>> DiG 9.21.0-dev <<>> nameserver2.mc.duke.edu aaaa
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19848
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: 662d3c7183a5df740100000066ecc74855728ea060130e36 (good)
;; QUESTION SECTION:
;nameserver2.mc.duke.edu. IN AAAA

;; AUTHORITY SECTION:
mc.duke.edu. 3283 IN SOA nc1-bc-hm1.dhe.duke.edu. hostmaster.dhe.duke.edu. 635464169 1200 180 1209600 3600

;; Query time: 0 msec
;; SERVER: ::1#53(::1) (UDP)
;; WHEN: Fri Sep 20 10:52:24 AEST 2024
;; MSG SIZE rcvd: 142

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