Domain reputation is the trust level mailbox providers assign a sending domain based on its authentication, sending volume history, and how recipients react, re-scored on every send rather than set once at setup.
Mailbox providers score a sending domain adaptively, on three inputs: authentication status, whether SPF, DKIM, and DMARC are in place and passing; sending volume relative to that domain's own history; and how recipients react, opens, replies, and complaints. A domain doesn't earn a reputation once and keep it. Every send feeds the score again.
None of the major providers' published sender guidelines describe detecting AI-written text as a scored signal, despite how often that gets assumed. What they document instead is identity, volume, and reaction, the three inputs above. That's also why a rushed, unwarmed domain gets flagged for behaving like a stranger sending a sudden burst of mail, regardless of how good the writing inside it is.
Reputation isn't a one-time setup, even though authentication is. SPF, DKIM, and DMARC get configured once per domain. Reputation gets re-scored on every send after that, filter models retrain on their own schedule, and any new domain or mailbox added later starts back at zero, no matter how well the rest of a sending program is running.
Cold-sending domains stay separate from a company's main domain specifically so a reputation problem in outbound never touches the domain a business actually depends on. Most real reputation problems trace back to skipped fundamentals, missing authentication, no real warmup, an unverified list, not some hidden algorithm change.
People look for a single mysterious cause, a secret word list, an AI-detection model, a specific competitor sabotaging their sends, when the documented mechanisms are only ever identity, volume, and reaction. The other common mistake is treating reputation as something fixed at domain setup instead of something re-earned, or lost, with every batch that goes out afterward.
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