Sender reputation, explained

Sender reputation is the trust score mailbox providers assign to your sending domain and IP addresses. It decides whether your mail lands in the inbox, the spam folder, or nowhere at all.

What feeds the score

• Bounce rate. High invalid-address rates signal poor acquisition. See email bounce rate.
• Complaint rate. Above 0.1% ("this is spam") is a red line at Gmail and Microsoft.
• [Spam trap](/learn/spam-traps) hits. The heaviest single penalty.
• Engagement. Opens, clicks, replies, and moves out of spam raise reputation; deletions without reading lower it.
• Authentication. SPF, DKIM and DMARC alignment are now mandatory for bulk senders.
• Volume consistency. Sudden spikes from a cold domain look like a compromised account.
• Infrastructure age. New domains and IPs start neutral-to-negative and must be warmed.

Domain vs IP reputation

Domain reputation follows you across ESPs and matters most for shared-IP senders. IP reputation matters most on dedicated IPs. If you switch ESPs, your domain reputation travels with you — a bad history is not erased by new infrastructure.

Practical protection checklist

• Authenticate: SPF, DKIM, and DMARC at least at p=none, moving to enforcement.
• Verify every address at capture and re-verify lists older than 90 days.
• Suppress hard bounces permanently, on the first bounce.
• Make unsubscribing one click and honour it immediately — burying it drives complaints.
• Warm new domains and IPs gradually over 4–6 weeks.
• Sunset unengaged contacts rather than mailing them "one more time".
• Separate transactional and marketing streams onto different subdomains.

Monitor with Google Postmaster Tools and Microsoft SNDS. Reputation drops show up there days before revenue drops show up in your dashboard.

Recovering after damage

Stop mailing the broad list. Verify everything, rebuild a send list from contacts who engaged in the last 90 days, mail that segment consistently for several weeks, then expand slowly. There is no faster route — providers score on trend, not promises.