spf-out.a1.at has no MX records.
Question and response
Question
dig spf-out.a1.at. MX
Answer
The response has no answer records.
Authority
a1.at. 3600 SOA dns1.a1.net. domainadmin.a1.net. 2026020503 10800 3600 1814400 3600
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0