mailint.sdt.net has no MX records.
Question and response
Question
dig mailint.sdt.net. MX
Answer
The response has no answer records.
Authority
sdt.net. 3600 SOA ns1.sdt.net. hostmaster.sdt.net. 2025103003 28800 7200 2419200 3600
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0