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

Results forspf.rpost.net

Resolver

Location

TXT

Name	TTL	Value
spf.rpost.net	300	v=spf1 ip4:54.67.101.6 ip4:3.101.2.139 ip4:18.194.112.42 ip4:52.58.131.9 ip4:52.58.136.115 ip4:52.58.128.109 ip4:18.197.195.173 ip4:54.215.254.223 ip4:184.178.75.213 ip4:3.64.36.62 ip4:3.126.115.75 ip4:54.176.66.31 ip4:54.176.246.82 ~all