mobi has no MX records.
Question and response
Question
dig mobi. MX
Answer
The response has no answer records.
Authority
mobi. 3600 SOA a0.mobi.afilias-nst.info. hostmaster.donuts.email. 1771814730 7200 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0