forward600b.mail.yandex.net has no TXT records.
Question and response
Question
dig forward600b.mail.yandex.net. TXT
Answer
The response has no answer records.
Authority
mail.yandex.net. 300 SOA ns3.yandex.ru. sysadmin.yandex.ru. 1772921983 900 600 3600000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0