It can be anything! An apex, subdomain, or even a URL.

Results forspf.smtp.cz

Resolver

Location

TXT

Name	TTL	Value
spf.smtp.cz	3600	v=spf1 ip4:81.95.97.0/25 ip4:81.95.105.128/26 ip4:185.12.196.0/24 ip4:81.95.96.15 ip4:81.95.96.29 ip6:2a02:4a8:ac24:101::/64 ip6:2a02:4a8:ac24:126::/64 ip6:2a02:4a8:ac24:130::/64 ip6:2a02:4a8:ac24:100::96:15