smtp.sfera.net has no MX records.
Question and response
Question
dig smtp.sfera.net. MX
Answer
The response has no answer records.
Authority
sfera.net. 3600 SOA dns.sfera.net. hostmaster.dns.sfera.net. 2019033293 3600 1800 3600000 3600
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0