mail.domain24.com has no MX records.
Question and response
Question
dig mail.domain24.com. MX
Answer
The response has no answer records.
Authority
domain24.com. 300 SOA dns.dns1.de. hostmaster.internetwire.de. 2014020501 28800 7200 604800 300
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0