ns3.systemdns.com has no MX records.
Question and response
Question
dig ns3.systemdns.com. MX
Answer
The response has no answer records.
Authority
systemdns.com. 300 SOA ns1.tucows.com. hostmaster.systemdns.com. 1771766669 10800 3600 2592000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0