coltsource.de.colt.net has no MX records.
Question and response
Question
dig coltsource.de.colt.net. MX
Answer
The response has no answer records.
Authority
de.colt.net. 3600 SOA ns0.de.colt.net. hostmaster.de.colt.net. 2010120210 10800 3600 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0