spf.uberspace.de has no MX records.
Question and response
Question
dig spf.uberspace.de. MX
Answer
The response has no answer records.
Authority
uberspace.de. 600 SOA ns1.jonaspasche.com. hostmaster.uberspace.de. 1771737991 1800 300 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0