How do ISPs view different subdomains under one root domain?

ISP treatment of subdomains:

Separate tracking:

Subdomains can build own reputation

Engagement and complaints tracked per subdomain

Different subdomains can have different standings

Root domain influence:

Severe root domain issues may affect subdomains

New subdomains may inherit some root reputation

Not completely independent

Provider variations:

Different providers weight root vs subdomain differently

Gmail more granular in tracking

Some may aggregate more

Practical effect:

Subdomains provide useful isolation

But not complete firewall

Better than no isolation

Divisions of a company have their own performance records but the parent company reputation still matters.