Sender reputation: what it actually is and where to read it now

Your sender reputation is not a score you can look up. Each mailbox provider maintains its own internal assessment of your sending domain, your IP, your authentication history and your content, recomputed constantly from how recipients treat your mail. Third-party "sender score" tools are estimates built from the data those vendors can see, which is a fraction of what Gmail or Microsoft sees. Treat them as a smoke alarm, never as the measurement.

What the providers actually weigh

Ranked roughly by how much they move the outcome:

1. Complaints. Someone pressing "report spam" is the strongest negative signal there is, and it is weighted per-recipient-provider. Google publishes 0.3% as the threshold bulk senders must stay under in Postmaster Tools, and recommends staying below 0.1%.
2. Engagement. Opens matter less than people think; replies, moves out of Junk, and adding you to contacts matter much more. Deletion without reading is mildly negative. No interaction at all, repeatedly, is quietly corrosive.
3. Invalid recipients. A high hard-bounce rate says you did not know who you were mailing. Keep hard bounces under 1%, and treat anything over 2% as a list problem to fix before you tune anything else.
4. Spam traps. Pristine traps — addresses that never opted in to anything — are the ones that cause sharp drops, because hitting one is proof of harvesting or purchase.
5. Authentication and consistency. SPF and DKIM passing and aligned, a stable sending infrastructure, and a volume curve that does not jump by an order of magnitude overnight.
6. Content and link reputation. Mostly it is the domains in your links, including tracking and redirect domains, which carry their own reputation independently of yours.

Where you can still read something real

The retirement of the Postmaster reputation chart changed how this question gets answered. There is no longer a "High / Medium / Low / Bad" label to screenshot. The substitute is a pair: Gmail spam rate from Postmaster Tools, and per-provider seed placement for everything else. That is a better instrument in practice, because it is measured on your mail rather than inferred from a label — but it means reputation is now something you trend, not something you look up.

Reading it without over-reading it

Reputation is per-provider and per-stream. It is entirely normal to sit at 95% inbox at Gmail and 40% at Outlook, because the two use different signals and your recipient mix differs. It is also normal for a domain to be fine while one mailbox on it is not — compromised or badly behaved individual mailboxes are common, which is why per-mailbox tracking is worth more than a domain-level summary.

Changes lag. A list cleanup or a complaint fix shows up over one to three weeks, not overnight, because providers weight recent behaviour against accumulated history. If you change something and the number moves the same afternoon, you probably changed the measurement rather than the reputation.

What not to do

Do not chase a vendor score as a KPI. Teams spend quarters moving a number that no mailbox provider reads. Do not buy engagement to lift it. Beyond being dishonest, it is now actively risky: Validity launched the Heatwave blocklist on 3 September 2026, specifically targeting synthetic reputation warming — networks of controlled mailboxes manufacturing opens, clicks and replies. It lists domains rather than IPs, launched with over a million of them, and feeds live filtering, with lookup at lookup.validity.tools and review via its /delist path. The thresholds are not public, so nobody — no tool, ours included — can tell you what keeps a domain off it.

Do not fix reputation by moving to a new domain. You lose the history that makes you deliverable and you take on the suspicion that attaches to brand-new domains. Do not keep mailing unengaged segments to "stay top of mind": unengaged recipients are where complaints and traps live. And do not treat a clean blocklist check as good news — most reputation damage never produces a listing at all.

The short version of fixing it

Stop sending to addresses that bounce or never engage. Make unsubscribing trivial and honour it immediately, including one-click unsubscribe headers on bulk mail. Get SPF, DKIM and DMARC aligned and keep SPF under ten DNS lookups. Split transactional, marketing and outbound onto separate domains or subdomains so one stream cannot sink the others. Hold volume steady rather than spiky. Then wait, and measure weekly.

MailPilot tracks the parts of this that are actually measurable: per-mailbox reputation recorded daily, real per-provider inbox placement from a seed network, and SPF, DKIM and DMARC checks on every connected domain — so when placement moves you can see which mailbox, which provider, and which day.