_spf.uni-ulm.de has no CNAME records.
Question and response
Question
dig _spf.uni-ulm.de. NS
Answer
The response has no answer records.
Authority
uni-ulm.de. 3600 SOA dns1.uni-ulm.de. hostmaster.uni-ulm.de. 2026030100 21600 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0