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

Results for_spf.shell.com

Resolver

Location

TXT

Name	TTL	Value
_spf.shell.com	300	v=spf1 ip4:205.239.80.10/31 ip4:185.189.236.215 ip4:87.253.238.200 ip4:87.253.238.201 ip4:37.98.232.26 ip4:134.145.189.4 ip4:134.145.75.4 ip4:148.163.135.62 ip4:148.163.139.98 ip4:52.28.190.192 ip4:52.28.134.198 -all