esmtp.simlab.net has no CNAME records.
Question and response
Question
dig esmtp.simlab.net. NS
Answer
The response has no answer records.
Authority
simlab.net. 1355 SOA ns1.megapath.com. support.megapath.com. 1734984407 7200 300 604800 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0