ntp01.ipfire.org has no MX records.
Question and response
Question
dig ntp01.ipfire.org. MX
Answer
The response has no answer records.
Authority
ipfire.org. 300 SOA master.lwldns.net. hostmaster.ipfire.org. 2026025597 10800 1800 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0