mobilemail.cs3g.com has no MX records.
Question and response
Question
dig mobilemail.cs3g.com. MX
Answer
The response has no answer records.
Authority
cs3g.com. 300 SOA ns1.p201.dns.oraclecloud.net. hostmaster.cs3g.com. 201205082 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0