How do ISPs use reverse DNS in trust scoring?

ISP trust scoring with rDNS:

Existence check: No PTR = immediate trust penalty or rejection.

Quality check:

Generic (dhcp-192-0-2-1.isp.net) = residential/dynamic IP = spam signal

Meaningful (mail.tidalmail.com) = professional server = trust boost

FCrDNS check: Forward confirmation adds confidence. Mismatch raises flags.

Combined scoring: rDNS feeds into overall reputation calculations alongside authentication, engagement, complaints.

Gate function: Some ISPs reject at connection if rDNS fails. Others accept but penalize heavily in filtering.

rDNS is a baseline requirement. Failure is disqualifying.

Initial document check before harbor entry. Failed inspection means restricted access or denied entry.