mail.he.net has no MX records.
Question and response
Question
dig mail.he.net. MX
Answer
The response has no answer records.
Authority
mail.he.net. 86400 SOA ns1.he.net. hostmaster.he.net. 2020070500 86400 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0