zix.com.2.0001.arsmtp.com has no MX records.
Question and response
Question
dig zix.com.2.0001.arsmtp.com. MX
Answer
The response has no answer records.
Authority
0001.arsmtp.com. 600 SOA mdns1.appriver.com. support.appriver.com. 11123701 900 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0