rs21.luxscioffice.com has no MX records.
Question and response
Question
dig rs21.luxscioffice.com. MX
Answer
The response has no answer records.
Authority
luxscioffice.com. 300 SOA dns1.easydns.com. zone.easydns.com. 1767395959 86400 43200 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0