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

Results formail3.securityiqmail.net

Resolver

Location

TXT

Name	TTL	Value
mail3.securityiqmail.net	300	v=spf1 +mx +ip4:52.1.22.105 +ip4:34.202.49.109 +ip4:54.155.87.88 +ip4:54.75.182.245 +ip4:3.19.93.167 +ip4:3.129.152.227 +ip4:52.72.211.23 +ip4:3.222.57.146 +ip4:159.135.238.30 ~all