mx.yandex.net has no TXT records.
Question and response
Question
dig mx.yandex.net. TXT
Answer
The response has no answer records.
Authority
yandex.net. 900 SOA ns1.yandex.net. hostmaster.yandex.net. 2023054868 600 300 1209600 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0