_net2.fortress.org has no MX records.
Question and response
Question
dig _net2.fortress.org. MX
Answer
The response has no answer records.
Authority
fortress.org. 3600 SOA ns.pubnix.net. purple.fortress.org. 2025010501 10800 300 2419200 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0