proxy04.lsn.net has no MX records.
Question and response
Question
dig proxy04.lsn.net. MX
Answer
The response has no answer records.
Authority
lsn.net. 300 SOA ns3.lsn.net. root.lsn.net. 2025040101 10800 3600 604800 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0