internal-mail-dca2.accountis.net has no MX records.
Question and response
Question
dig internal-mail-dca2.accountis.net. MX
Answer
The response has no answer records.
Authority
accountis.net. 60 SOA accountis.net. sysadmin.fsc.accountis.net. 2016032160 60 900 1209600 42300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0