mail.FLEXLINE.RU has no MX records.
Question and response
Question
dig mail.FLEXLINE.RU. MX
Answer
The response has no answer records.
Authority
FLEXLINE.RU. 3600 SOA ns4.FLEXLINE.RU. root.FLEXLINE.RU. 2025092501 10800 7200 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0