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

Results forspf.seg.trustwave.com

Resolver

Location

TXT

Name	TTL	Value
spf.seg.trustwave.com	600	v=spf1 ip4:52.165.84.32/28 ip4:52.165.84.16/28 ip4:20.81.235.112/28 ip4:20.81.235.96/28 ip4:20.98.138.168/30 ip4:20.49.58.108/30 ip4:204.13.200.0/22 ip4:208.90.236.0/22 -all