mx2.arsmtp.com has no MX records.
Question and response
Question
dig mx2.arsmtp.com. MX
Answer
The response has no answer records.
Authority
mx2.arsmtp.com. 600 SOA mdns1.appriver.com. support.appriver.com. 11121073 900 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0