mx3.zctracker.com has no MX records.
Question and response
Question
dig mx3.zctracker.com. MX
Answer
The response has no answer records.
Authority
zctracker.com. 600 SOA ns1.zohocorp.com. dnsadmin.vtitan.com. 2026022201 7200 1800 1209600 3600
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0