rydal-group.co.uk.2.0001.arsmtp.com has no MX records.
Question and response
Question
dig rydal-group.co.uk.2.0001.arsmtp.com. MX
Answer
The response has no answer records.
Authority
0001.arsmtp.com. 600 SOA mdns1.appriver.com. support.appriver.com. 11135714 900 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0