Sender reputation
Sender reputation is the running score every mailbox provider keeps on your sending domain and IP, derived from engagement, complaints, bounces, and spam-trap hits.
- n/a — descriptive term
- Deliverability metric
- Reaching the inbox at any meaningful volume
- Diagnosing deliverability dips or planning a new send
What it is
Sender reputation is a private, internal scoring system that every mailbox provider — Gmail, Outlook, Yahoo, Apple iCloud, the corporate gateways — maintains for every domain and every IP it has ever seen send mail. The scores are not published. There is no API to query them. The closest external proxies are Google Postmaster Tools and Microsoft SNDS, both of which expose buckets ("High", "Medium", "Low", "Bad") rather than raw numbers.
How it works
The score is computed continuously from a handful of inputs. Positive: opens, replies, drag-out-of-spam actions, time spent reading, "mark as important", forwards. Negative: spam complaints, deletions without opening, hard bounces, soft bounces past threshold, and the worst single hit available — spam-trap addresses. The window is usually 30–90 days, weighted toward recent events.
Crucially, reputation is partitioned. Gmail does not share its score with Outlook. A clean reputation at Yahoo will not save you at Microsoft. Each provider holds its own ledger, which is why deliverability problems often look provider-shaped — fine at one, broken at another.
Why it matters
Reputation is the gating function before content filters even read your message. A bad reputation at Gmail means even a perfect email goes to spam. A good reputation buys you forgiveness when a single campaign underperforms. It is also slow to build and fast to lose — a single 5% complaint rate can shred months of patient warmup in a weekend.
Reputation is the half of deliverability that email warmup directly addresses. The other half — content reputation — is what template-based warmup was built for.