ns6.oleane.net has no MX records.
Question and response
Question
dig ns6.oleane.net. MX
Answer
The response has no answer records.
Authority
oleane.net. 600 SOA ns6.oleane.net. admp-ess-imap.oleane.net. 2015066273 14400 2000 2500000 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0