Sender reputation
The trust score mailbox providers assign to your domain and IP, driving inbox placement.
Sender reputation is the trust score that mailbox providers (Gmail, Outlook, Yahoo, Apple) assign to your sending domain and IP. Higher reputation means better inbox placement; lower reputation means filtering, spam-folder placement, or outright rejection.
Reputation is calculated from many signals: authentication setup (SPF/DKIM/DMARC), engagement metrics (opens, clicks, replies, "not spam" marks), complaint rates (recipients marking as spam), bounce rates, unsubscribe patterns, sending volume consistency, and complaint feedback loops with the ISPs themselves. The exact algorithms are proprietary and continuously tuned.
Reputation is hyperlocal. Your Gmail reputation is independent of your Outlook reputation, which is independent of your Yahoo reputation. A deliverability problem at one provider doesn't necessarily mean a problem at another. Monitoring tools (Google Postmaster Tools for Gmail, Microsoft SNDS for Outlook) expose per-provider reputation metrics; healthy senders monitor these continuously.