Domain reputation: how mailbox providers score you
The single most important variable in whether your email reaches the inbox. What domain reputation is, how Gmail, Outlook, and Yahoo compute it, and how to repair it after a bad campaign.
Domain reputation is the rolling score that mailbox providers like Gmail and Outlook maintain on your sending domain. It is built from engagement (opens, replies, moves to inbox), complaints, bounces, authentication, and sending pattern. Check it with Google Postmaster Tools, Microsoft SNDS, Talos Intelligence, and MXToolbox. Improve it with warmup, list hygiene, and consistent sending. Recovery from damage takes 6–12 weeks.
What is domain reputation?
Domain reputation is the rolling score that mailbox providers maintain on your sending domain — the part after the @ in your From address. Every time you send a message, the receiving provider updates this score based on what the recipient does with the message and what the system detects about it.
The score is private. Providers do not publish a number you can query directly. Gmail exposes a coarse bucket ("Bad / Low / Medium / High") in Postmaster Tools. Microsoft exposes complaint and trap-hit data in SNDS. Third parties like Talos Intelligence and Sender Score derive their own score from receiver-side signals and SMTP behavior.
The score is provider-specific. Your Gmail domain reputation is independent from your Outlook reputation. A good Gmail score does not guarantee Outlook placement.
Why sender domain reputation matters more than IP reputation
Ten years ago, IP reputation was the dominant variable. Most senders used dedicated IPs, and SMTP-layer reputation traveled with the IP. That world is gone.
In 2026, the average commercial sender uses a shared IP at an ESP (SendGrid, Postmark, Amazon SES, Google Workspace, Microsoft 365). The IP carries dozens or thousands of other senders. IP reputation is a noisy floor signal — you can't differentiate yourself with it. Sender domain reputation is the part you actually own.
In Gmail's public guidance, domain reputation is weighted more heavily than IP reputation for senders below ~10,000 messages/day. Above that volume, both matter — but domain is still primary.
How mailbox providers score your domain
Each provider runs its own ML model. The published guidance and observed behavior converges on roughly these inputs:
- Positive engagement. Opens that lead to replies, "move to inbox", "mark not spam", archive after read, forward.
- Negative engagement. Delete-without-read, "report spam", unsubscribe, "move to spam".
- Complaint rate. Spam complaints per message sent. Threshold for trouble: ~0.1%; threshold for serious damage: 0.3%+.
- Bounce profile. Hard bounce rate, soft bounce rate, ratio of recipients-never-seen.
- Spam-trap hits. Sending to recycled or pristine traps. Catastrophic on Spamhaus.
- Authentication consistency. SPF (RFC 7208), DKIM (RFC 6376), and DMARC (RFC 7489) all aligned.
- Sending pattern. Consistent daily volume scores better than bursty patterns.
- Domain age and history. Older domains with clean history have a higher trust ceiling.
- Content fingerprint. Template-level reputation independent of sender — see template-based warmup.
Domain reputation Gmail specifics
Gmail is the most documented provider, and the one most cold senders optimize for. Domain reputation Gmail is exposed in Postmaster Tools as one of four buckets:
| Bucket | Inbox placement | Action |
|---|---|---|
| High | Nearly always inbox | Maintain volume and engagement |
| Medium | Mostly inbox; some spam | Improve engagement; trim list |
| Low | Frequent spam-foldering | Pause; audit; remediate |
| Bad | Most mail to spam or blocked | Stop sending; full remediation |
Postmaster requires 100+ messages/day to show data. If you're sub-threshold, run warmup to surface data, then compare against your real campaign output.
How to check your domain reputation
An email domain reputation check in 2026 means triangulating across four sources. Use all of them — no single one is authoritative.
- Google Postmaster Tools — postmaster.google.com. The single most important source. Shows Gmail domain reputation bucket, IP reputation, authentication pass rates, spam complaint rate, encryption rate, and delivery errors. Requires DNS verification.
- MX Toolbox — mxtoolbox.com. Blacklist lookups across 100+ RBLs, DNS validation, SPF/DKIM/DMARC syntax checks. Catches Spamhaus listings within hours.
- Talos Intelligence — talosintelligence.com. Cisco's domain and IP reputation reading. Used by enterprise spam filters. Three buckets: Good / Neutral / Poor.
- Sender Score — senderscore.org. Validity's 0–100 score for IPs and domains. Imperfect but useful as a third reading. We explain it in detail in our sender score explained post.
For Outlook specifically, add Microsoft SNDS. For seed-test data, run an inbox placement test.
How to improve domain reputation
The mechanics of how to improve domain reputation are straightforward — generate more positive engagement, fewer negative signals, and keep authentication aligned. The work is in the consistency.
- Fix authentication first. SPF, DKIM, DMARC. Run an SPF check and a DMARC validator. Aim for DMARC p=quarantine minimum.
- Validate the list. Drop bouncers, risk-score >5%, and role addresses if you can.
- Warm the domain. 2–4 weeks of consistent engagement on a new or recovering domain. Use template-based warmup so the engagement applies to your actual campaign template.
- Send consistently. Daily volume in a narrow range beats burst patterns. Don't do 0 emails for a week then 5,000 in a day.
- Match identities. From domain, Reply-To domain, DKIM signing domain, and link domains should all align with your sending domain.
- Add one-click unsubscribe. RFC 8058 List-Unsubscribe-Post header. Required for Gmail bulk sender rules.
- Suppress fast. Hard bounces and complaints get permanently suppressed. No exceptions.
Recovering a damaged domain
If Postmaster shows "Low" or "Bad", you're past the point where tuning helps. Time for remediation.
- Week 1. Stop all production sends. Audit authentication. Check blacklists.
- Week 2. Validate the entire list. Drop anything risky. Set up Postmaster and SNDS if not already.
- Week 3–6. Run template-based warmup at low daily volume. Monitor Postmaster daily.
- Week 7+. Resume sends at 10% of pre-incident volume. Ramp 25% per day if reputation stays "Medium" or improves.
- Ongoing. If recovery stalls past 12 weeks, consider rotating to a fresh sending subdomain (e.g., mail2.yourbrand.com). The parent brand domain stays clean for transactional mail.
Frequently asked questions
What is domain reputation?
Domain reputation is the score mailbox providers maintain on your sending domain. It is built from sender behavior over time — engagement (opens, replies, "move to inbox"), complaints, bounces, spam-trap hits, authentication consistency, and sending volume patterns. Providers use this score, along with content and IP signals, to decide whether incoming mail lands in the inbox, spam folder, or gets rejected at SMTP.
How do I check my domain reputation?
Use Google Postmaster Tools for Gmail domain reputation, Microsoft SNDS for Outlook IP and complaint data, Talos Intelligence for a third-party domain score, and Sender Score for a 0–100 rating across receivers. No single tool is authoritative — triangulate across at least two. Seed tests (sending to 30+ test inboxes and counting placement) are the only true measure of inbox placement.
How long does it take to improve domain reputation?
A clean, properly warmed domain can build a "Medium" Gmail Postmaster score in 2–4 weeks and "High" in 6–8 weeks of consistent engagement. A damaged domain takes longer: 6–12 weeks of remediation depending on how badly it was burned. Reputation has time-decay built in — old behavior fades, but recent behavior dominates.
Does sending volume affect domain reputation?
Yes, but pattern matters more than absolute volume. Consistent daily volume builds reputation. Bursty patterns — quiet for weeks then 10,000 emails in one day — flag as suspicious regardless of total volume. Gmail and Outlook both model sending velocity and penalize anomalies, especially on younger domains.
What is the difference between domain reputation and IP reputation?
Domain reputation is tied to the domain in your From address. IP reputation is tied to the sending server's IP address. Gmail and Yahoo rely more heavily on domain reputation; Outlook weighs IP reputation more. If you use a shared IP at an ESP (typical), domain reputation is the one you actually control — and the one that follows you to a new IP.
Can a subdomain have separate reputation from the parent domain?
Mostly yes, with caveats. Mailbox providers track subdomain reputation independently for engagement and complaint metrics, but severe parent-domain issues (blacklist listings, DMARC failures) cascade to subdomains. Using subdomains like mail.yourbrand.com to isolate cold outreach from transactional traffic is standard practice and works in 2026.
Does email warmup improve domain reputation?
Yes, when the warmup generates real engagement signal that mailbox providers count. The catch: most warmup tools warm with synthetic templates, so the reputation built does not transfer cleanly when you switch to your actual cold campaign. Template-based warmup applies the engagement signal to the body you actually ship, closing that gap.
Keep reading
All posts ↗- Sender Score Explained: What It Is, How to Improve ItSender Score is a 0-100 IP reputation number from Validity. Here is what it actually measures, when it matters, when it does not, and how to improve it.
- Soft Bounce vs Hard Bounce: What Actually DiffersSoft bounce vs hard bounce — SMTP 4xx vs 5xx, why one is temporary and one is permanent, retry policy, and how each affects sender reputation.
- Cold Email vs Marketing Email: The Real DifferencesCold email vs marketing email — different intent, different infrastructure, different rules, and why mixing them on one domain kills deliverability.
- Email Warmup in 2026: The Complete GuideThe 2026 email warmup guide — what warmup actually does, how mailbox providers measure it, why sender-only warmup falls short, and the playbook that works now.