Ok so I ran the same command you did against a local copy of my software as well as my production name servers and everything works as expected.
Maybe there's a problem somewhere in the middle?
dig @ns1.callahtech.com +trace +bufsize=512 mail.callahtech.com
; <<>> DiG 9.16.1-Ubuntu <<>> @ns1.callahtech.com +trace +bufsize mail.callahtech.com
; (1 server found)
;; global options: +cmd
. 300 IN NS ns1.callahtech.com.
. 300 IN NS ns2.callahtech.com.
;; Received 79 bytes from 98.213.184.202#53(ns1.callahtech.com) in 25 ms
mail.callahtech.com. 300 IN CNAME safari.mxrouting.net.
;; Received 90 bytes from 98.213.184.202#53(ns1.callahtech.com) in 21 ms
-----------------------------------------------------------------------------------------
dig @ns2.callahtech.com +trace +bufsize=512 mail.callahtech.com
; <<>> DiG 9.16.1-Ubuntu <<>> @ns2.callahtech.com +trace +bufsize mail.callahtech.com
; (1 server found)
;; global options: +cmd
. 300 IN NS ns2.callahtech.com.
. 300 IN NS ns1.callahtech.com.
;; Received 79 bytes from 35.231.196.113#53(ns2.callahtech.com) in 46 ms
mail.callahtech.com. 300 IN CNAME safari.mxrouting.net.
;; Received 90 bytes from 98.213.184.202#53(ns1.callahtech.com) in 26 ms
-----------------------------------------------------------------------------------------
dig @192.168.73.1 +trace +bufsize=512 mail.callahtech.com
; <<>> DiG 9.16.1-Ubuntu <<>> @192.168.73.1 +trace +bufsize mail.callahtech.com
; (1 server found)
;; global options: +cmd
. 300 IN NS ns1.callahtech.com.
;; Received 48 bytes from 192.168.73.1#53(192.168.73.1) in 2 ms
mail.callahtech.com. 300 IN CNAME safari.mxrouting.net.
;; Received 90 bytes from 98.213.184.202#53(ns1.callahtech.com) in 22 ms
I also enabled TCP connections on both name servers / adjusted firewall rules
dig +tcp +trace +bufsize=512 mail.callahtech.com
; <<>> DiG 9.16.1-Ubuntu <<>> +tcp +trace +bufsize mail.callahtech.com
;; global options: +cmd
. 42032 IN NS a.root-servers.net.
. 42032 IN NS k.root-servers.net.
. 42032 IN NS c.root-servers.net.
. 42032 IN NS e.root-servers.net.
. 42032 IN NS f.root-servers.net.
. 42032 IN NS j.root-servers.net.
. 42032 IN NS g.root-servers.net.
. 42032 IN NS d.root-servers.net.
. 42032 IN NS h.root-servers.net.
. 42032 IN NS m.root-servers.net.
. 42032 IN NS b.root-servers.net.
. 42032 IN NS i.root-servers.net.
. 42032 IN NS l.root-servers.net.
. 42032 IN RRSIG NS 8 0 518400 20210428050000 20210415040000 14631 . VAN9EL8cU10Xk+mcU4q/t0W3EZ4iS/YJ/gmAVuIhTCmuQQcFEN0++99t T1oVdJWRtSQBMoaLbliwEOtEb5tJ5aEsYJB1gzVWTRQrP9IKK2CGoOYL u8sMSoJFz1VEbwG+HGtkK9QFW4PI7TucPkHSgTIJCJO3q8UqIvP4Nmd6 mB+jKgrz11vKDzQgSZBHFOMYgrq8MiG8R+dU/lc5gVIpyUDYBiZXvFhB v9Fl7wwiCHf0oe7kp8Zeo5VEzgEgepXuGfiHx1dA32FbMiWXNMhxsmlJ MaGrQ754BE/0hkNSRA7afsuKTWvRi3qdSePJf4HSAVmVQp/t703xjSui /twc+A==
;; Received 1111 bytes from 10.1.2.4#53(10.1.2.4) in 26 ms
;; Connection to 2001:500:1::53#53(2001:500:1::53) for mail.callahtech.com failed: connection refused.
;; Connection to 2001:500:200::b#53(2001:500:200::b) for mail.callahtech.com failed: connection refused.
com. 172800 IN NS c.gtld-servers.net.
com. 172800 IN NS j.gtld-servers.net.
com. 172800 IN NS k.gtld-servers.net.
com. 172800 IN NS b.gtld-servers.net.
com. 172800 IN NS d.gtld-servers.net.
com. 172800 IN NS f.gtld-servers.net.
com. 172800 IN NS l.gtld-servers.net.
com. 172800 IN NS e.gtld-servers.net.
com. 172800 IN NS h.gtld-servers.net.
com. 172800 IN NS i.gtld-servers.net.
com. 172800 IN NS m.gtld-servers.net.
com. 172800 IN NS g.gtld-servers.net.
com. 172800 IN NS a.gtld-servers.net.
com. 86400 IN DS 30909 8 2 E2D3C916F6DEEAC73294E8268FB5885044A833FC5459588F4A9184CF C41A5766
com. 86400 IN RRSIG DS 8 1 86400 20210428210000 20210415200000 14631 . Nq8NGgqWe3KvGbJpbOhwU5m2EPe2tZ3l4KLQ5Po2HZeTX/UMPihdRFmj MzHJlblQ5Nj1LyLT0y3R4tBP3C2yLUjZofetXT3Rk4R1qtanBMvIevi1 SEAi6EiEdXM7V4+GsVr3pmXuSCtrRJxd31KleTYSg2o0GjTs2y2ZEKIA h5d3n86sc1e9WLvsw7yGNRY5LRpce9p4vrzI5t51QOq8N0kqMn5D224M jFEu9Y88QWNOzkbHGpd7W8184QMjNSptLU2yEe93zMelvdmsj0e5UYwj ykE6mJWsXCnbZtqiw1iO03xWiaCMw0bb8AkOJN9dUZjXEgwPhRKeyDs/ Lg7eDw==
;; Received 1210 bytes from 192.36.148.17#53(i.root-servers.net) in 65 ms
;; Connection to 2001:500:d937::30#53(2001:500:d937::30) for mail.callahtech.com failed: connection refused.
callahtech.com. 172800 IN NS ns1.callahtech.com.
callahtech.com. 172800 IN NS ns2.callahtech.com.
CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN NSEC3 1 1 0 - CK0Q1GIN43N1ARRC9OSM6QPQR81H5M9A NS SOA RRSIG DNSKEY NSEC3PARAM
CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN RRSIG NSEC3 8 2 86400 20210422042410 20210415031410 58540 com. fePohSpUOL9K9eCljlIgjwl8TiSbS1ahDo0B1FI9aIIZA3u1AuzKQgzK yRxC56l4SXq5oLvuUe8Xti4/G8ARewoTTNtgNN0KWIj7PKCNdLDSQYtu nF3HoZZLtoKomKgq6YXbdwt9+6Qern+as2SAI2pWvPPjsGVx0400tCNY C1YgPGOuMomEm/Fg/aWwW6uv/a+k7SJPSKIvJ0CLHiCmuw==
H65L7M3MIGIV8R2KQCESNJ40P899F280.com. 86400 IN NSEC3 1 1 0 - H65L7OIBUMRA7PJ9OMCNLLC3US4O2KDT NS DS RRSIG
H65L7M3MIGIV8R2KQCESNJ40P899F280.com. 86400 IN RRSIG NSEC3 8 2 86400 20210420042850 20210413031850 58540 com. xiE7huTczKb9V2kdess7uuV2zH3heV/nhU9EEVl3KO5LeWPO5+o+WoRV 8fsi8MGx/Jm/2XH4FuhNXWVp6ue2bAgLJpH4LNhHqZP1oN71kgVmBu7d B5B3dVEH6Hq+EEFyG7OUoCFyAWRQq2+Bg/v+Y/nZinv9SrgKY2OYgJKS Lsuj8Crdt/3H4GysjDh7Mh2u9i09/swd0LUfSNQHaCH8GQ==
;; Received 665 bytes from 192.54.112.30#53(h.gtld-servers.net) in 54 ms
;; expected opt record in response
mail.callahtech.com. 300 IN CNAME safari.mxrouting.net.
;; Received 90 bytes from 35.231.196.113#53(ns2.callahtech.com) in 78 ms
It still doesn't work: https://unboundtest.com/m/A/mail.callahtech.com/QI3D22U6