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

Results forspf.viaduc.fr

Resolver

Location

TXT

Name	TTL	Value
spf.viaduc.fr	300	v=spf1 include:_mailcust.gandi.net ip4:195.154.236.140 mx:viaduc.fr ip4:178.32.254.234 ip4:176.31.218.45 ip4:178.32.254.229 ip4:46.105.108.101 ip4:5.135.106.4 ~all