Deliverability & the inbox
Sender reputation
Also known as: IP reputation · domain reputation
A per-IP and per-domain score mailbox providers use to decide whether to inbox, tab, or junk a sender's mail — driven mostly by complaint rate, bounce rate, engagement, and authentication alignment.
Sender reputation is the composite score mailbox providers maintain on every sending IP and every sending domain. Gmail, Outlook, Yahoo each have their own model, but the inputs overlap heavily: complaint rate (users hitting "mark as spam"), hard-bounce rate, engagement (opens, replies, forwards, out-of-folder moves), authentication alignment (SPF, DKIM, DMARC), and spam-trap hits. Reputation is measured at both IP and domain level — a clean IP on a poisoned domain still gets blocked. Reputation degrades faster than it recovers: one high-complaint send can drop you into Promotions or Spam for weeks, and rebuilding requires the same gradual engagement-first approach as warming a new IP. Google Postmaster Tools exposes Gmail reputation directly; other providers hide it behind inbox-placement tests.
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Reputation recovery: the 90-day playbook for dropping from High to Low
Domain reputation at Low or Bad isn't a problem you fix this week. It's a 6–12 week project of disciplined sending to engaged users only, while the reputation signals slowly reset. Here's the plan.
Domain vs IP reputation: which one actually matters
Deliverability reputation is two parallel scores, not one. IP and domain behave differently, recover differently, and the balance between them has shifted hard toward domain over the past five years. Here's what that means for what you monitor and how you warm up.