mx.tds.net has no MX records.
Question and response
Question
dig mx.tds.net. MX
Answer
The response has no answer records.
Authority
tds.net. 3600 SOA pv-dnsm.dns.tds.net. hostmaster.tds.net. 2025041776 21600 3600 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0