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

Results for_spf.sender4.xserver.jp

Resolver

Location

TXT

Name	TTL	Value
_spf.sender4.xserver.jp	3600	v=spf1 +ip4:183.181.94.185 +ip4:183.181.94.186 +ip4:183.181.94.187 +ip4:183.181.94.188 +ip4:183.181.99.207 +ip4:183.181.99.206 +ip4:183.181.99.208 +ip4:183.181.94.252 ~all