0001.arsmtp.com has no MX records.
Question and response
Question
dig 0001.arsmtp.com. MX
Answer
The response has no answer records.
Authority
0001.arsmtp.com. 600 SOA mdns1.appriver.com. support.appriver.com. 11121403 900 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0