ns1.layer6.net has no MX records.
Question and response
Question
dig ns1.layer6.net. MX
Answer
The response has no answer records.
Authority
layer6.net. 3600 SOA web-nl.itldc.com. mnt-by.itldc.com. 2019122186 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0