How do ISPs weigh authentication and reputation differently?
Providers weight signals differently:
Gmail: Engagement and domain reputation are primary. Authentication is table stakes. User behavior drives decisions.
Microsoft: IP reputation is heavily weighted. New IPs face significant friction. Authentication matters but IP history matters more.
Yahoo: Complaint rates are paramount. High complaints cause rapid filtering. Authentication is required but complaints override.
Understanding these differences helps diagnose provider-specific issues. A problem at one provider may not exist at others.
Each harbor prioritizes different inspection criteria. Know what each one cares about most.
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