ipv6.he.net has no MX records.
Question and response
Question
dig ipv6.he.net. MX
Answer
The response has no answer records.
Authority
ipv6.he.net. 86400 SOA ns1.he.net. hostmaster.he.net. 2022091507 10800 3600 360000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0