ruby.rubycom.com has no MX records.
Question and response
Question
dig ruby.rubycom.com. MX
Answer
The response has no answer records.
Authority
rubycom.com. 300 SOA ns1.dnsrubycom.com. equiposoporte.rubycom.com. 2025101101 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0