Domain reputation is the cumulative result of every email sent from your domain — the ratio of engaged recipients to spam complaints, the sending volume consistency, the age of the domain, and the blacklist status across the major reputation databases. The agent monitors all these signals continuously: spam complaint rate (the single most influential deliverability metric), blacklist status across 100+ reputation databases, SPF, DKIM, and DMARC record validity, domain warmup progress for new sending domains, and reputation scores from Google Postmaster Tools and Microsoft SNDS. Issues are detected in real time — a blacklist listing or DMARC record misconfiguration is caught within 24 hours, not discovered when a campaign's open rate drops to 4%.

Aggregate open rates hide provider-specific deliverability problems. If Gmail open rates are 28% but Outlook open rates are 6% for the same campaign, you have a provider-specific placement issue — likely a spam filter trigger or a reputation problem with Microsoft's filtering infrastructure specifically. The agent breaks down engagement metrics by mailbox provider (Gmail, Outlook/Microsoft 365, Yahoo, Apple Mail, and corporate domains) and runs inbox placement tests to measure where emails actually land: primary inbox, promotions tab, spam folder, or not delivered at all. Provider-specific issues are flagged with the contributing factors — a Microsoft JUNK filter trigger looks different from a Gmail promotions tab classification, and the remediation is different for each.

Domain reputation damage usually starts with list hygiene problems — sending to invalid addresses, spam traps, and highly disengaged recipients who don't open or click anything. The agent audits the active sending list against these risk factors: email validation status (valid, risky, invalid), spam trap exposure across known trap networks, engagement age distribution (how many recipients haven't opened an email in 6+ months), unsubscribe handling compliance, and bounce rate by campaign. High-risk segments are flagged for suppression before they accumulate spam complaints. The audit also checks sending volume patterns for sudden spikes that mailbox providers interpret as spam signals — a 10x volume increase from an account that normally sends 500 emails per day is a red flag regardless of content quality.

A deliverability audit that ends with a list of problems and no ordered action plan is just an anxiety generator. The agent synthesizes all signals — reputation health, inbox placement, list hygiene issues, and infrastructure gaps — into a prioritized remediation plan ordered by impact on inbox placement. Critical issues (active blacklist listing, DMARC misconfiguration, spam trap exposure) are surfaced first with specific technical remediation steps. High-priority list hygiene recommendations follow, with estimated impact on spam complaint rate and inbox placement if addressed. Each item has an estimated effort rating and an expected outcome metric — so the team knows which changes to make first and what improvement to expect from each.