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

Results forahsmtp.plex.com

Resolver

Location

A

Name	TTL	Value
ahsmtp.plex.com	14400	65.161.25.58Plexus Systems LLC / Sprint

Name	TTL	Value
ahsmtp.plex.com	7200	v=spf1 ip4:38.97.236.0/24 ip4:65.161.25.0/24 ip4:66.35.58.128/26 -all