cta.successinet.com has no MX records.
Question and response
Question
dig cta.successinet.com. MX
Answer
The response has no answer records.
Authority
successinet.com. 3600 SOA ns1.successinet.com. hostmaster.successinet.com. 2018042516 10800 3600 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0