_spf.yandex.net has no MX records.
Question and response
Question
dig _spf.yandex.net. MX
Answer
The response has no answer records.
Authority
yandex.net. 900 SOA ns1.yandex.net. hostmaster.yandex.net. 2023054775 600 300 1209600 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0