mail.interdomain.net has no MX records.
Question and response
Question
dig mail.interdomain.net. MX
Answer
The response has no answer records.
Authority
interdomain.net. 300 SOA ns1.interdomain.net. admin.interdomain.net. 640338651 28800 7200 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0