How the reputation of your sending IP affects inbox placement — and what drives it up or down.
⚡ Monitored by EmailExacto IntelligenceIP reputation is the trustworthiness score assigned to a sending IP by ISPs, spam filters, and security providers based on observed sending behaviour. It's one of the primary signals mail servers use to decide whether to deliver to inbox, spam, or reject entirely. Each major provider maintains its own reputation model independently.
Receiving servers track metrics for every IP: complaint rates, hard bounce rates, spam trap hits, engagement rates, volume consistency, and blacklist status. These feed into reputation models updated continuously.
Reputation exists at two levels: shared IPs (used by multiple senders on an ESP) where your reputation is affected by others, and dedicated IPs where only your behaviour determines the score. Dedicated IPs require a warmup period to build reputation from scratch.
IP reputation is often the deciding factor in inbox vs. spam placement, especially at Outlook/Hotmail and Yahoo. Poor reputation causes bulk deferrals (421 errors) before escalating to hard blocks. New IPs with no history start with neutral-to-poor reputation until they establish a track record — why warmup is non-optional.
EmailExacto monitors IP reputations for all IPs associated with your sending domain, including DNSBL checks and inbox placement test results per provider.
✓Warm up new IPs gradually — start at 100-200 emails/day and double weekly for 4-6 weeks.
✓Keep complaint rates below 0.1% — above 0.3% triggers filtering at Gmail and Yahoo.
✓Maintain bounce rates below 2%.
✓Send consistently — erratic volume spikes are a spam signal.
✓Use separate IPs for transactional and marketing email.
✓Monitor Google Postmaster Tools and Microsoft SNDS for direct ISP reputation feedback.
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