_spf.ipfire.org has no MX records.
Question and response
Question
dig _spf.ipfire.org. MX
Answer
The response has no answer records.
Authority
ipfire.org. 300 SOA master.lwldns.net. hostmaster.ipfire.org. 2026025137 10800 1800 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0