mail2.sbt-group.com has no MX records.
Question and response
Question
dig mail2.sbt-group.com. MX
Answer
The response has no answer records.
Authority
sbt-group.com. 3600 SOA dns1.odn.de. netmaster.sellbytel.de. 2020040830 10800 3600 777600 3600
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0