oxygen.redexpertos.com has no MX records.
Question and response
Question
dig oxygen.redexpertos.com. MX
Answer
The response has no answer records.
Authority
redexpertos.com. 1800 SOA duke.ns.cloudflare.com. dns.cloudflare.com. 2397104192 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0