us3.hesk.com has no MX records.
Question and response
Question
dig us3.hesk.com. MX
Answer
The response has no answer records.
Authority
hesk.com. 180 SOA ns11.constellix.com. dns.constellix.com. 2015012072 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0