gold.foundationdns.net has no MX records.
Question and response
Question
dig gold.foundationdns.net. MX
Answer
The response has no answer records.
Authority
foundationdns.net. 1800 SOA blue.foundationdns.com. dns.cloudflare.com. 2397474191 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0