Sender reputation explained

Sender reputation is the judgment a mailbox provider forms about the IP addresses and domains your mail comes from, based on how that mail has behaved in the past. No provider publishes its formula, but they name the signals: whether the mail is authenticated, how often recipients report it as spam, how much of it goes to addresses that do not exist, whether it reaches spam traps, whether people engage with it, and whether volume stays steady. A good reputation gets mail into the inbox; a poor one gets it filtered as spam, deferred or refused. You can watch parts of it in Google Postmaster Tools, Microsoft SNDS and the public blocklists, and you rebuild it slowly, by fixing the cause and mailing only people who want your mail.

IP reputation and domain reputation

Providers keep a reputation for each sending IP address and for each sending domain. Yahoo's sender best practices say that every sending IP and every DKIM domain has its own reputation, and that a domain which authenticates with SPF, DKIM and DMARC keeps a consistent reputation whichever IP sends its mail. Google's email sender guidelines say Gmail tracks volume, feedback and limits per domain and per IP: the SPF and DKIM quotas belong to your domain, while the IP quota is shared by everyone who sends from that IP.

On a shared IP, Google adds, the activity of any sender affects the reputation of every sender on it. See shared vs dedicated IPs for when your own IP is worth it.

The balance between the two has shifted toward the domain. Spamhaus wrote in How does email reputation work? (2022) that, for inbox placement, the reputation of domains and content now matters more than IP reputation. One reason it gives: IPv6 hands spammers so many addresses that they can discard them cheaply. In practice this means a new IP does not rescue a domain with a bad record.

Keep your mail streams apart

Both Gmail and Yahoo ask you to separate kinds of mail. Yahoo wants marketing and bulk mail sent from different IPs than user, transactional and alert mail, so each stream keeps its own reputation. Google asks for a separate IP per message type if you use several IPs, and a consistent From: address per category, such as receipts, promotions and account alerts. More in transactional vs marketing email.

What providers judge it by

Authentication

Google says authenticated mail is less likely to be rejected or marked as spam. Microsoft's Outlook.com postmaster troubleshooting page lists authentication among the factors its filters weigh, next to the sending IP, the domain, list accuracy, complaints and content, and requires SPF, DKIM and DMARC from senders of more than 5,000 messages a day to Outlook.com. The details per provider are in the Gmail and Yahoo and Outlook requirements guides.

Spam complaints

Complaints are the signal providers stress most. Microsoft calls junk mail complaints one of the main factors that lower a sender's reputation. Google says spam reports lower your domain's reputation over time and make later messages more likely to land in spam.

Only Google and Yahoo publish numbers:

Microsoft's postmaster pages give no complaint threshold, and Spamhaus's sender guidelines set none either. A person who complains is telling you to stop; our results mark a known complainer as valid with the action remove for that reason (why complaints hurt).

Bounces and list accuracy

Mail to addresses that do not exist tells a provider your list is old or was not collected with care. Google asks you to lower volume when messages start bouncing and to unsubscribe recipients after repeated bounces. Yahoo asks you to watch hard and soft bounces and remove invalid recipients promptly. Spamhaus's sender guidelines are the only ones here with a number: keep the overall bounce rate below 5%, suppress hard bounces at once, and look into an address after about three to five soft bounces in a row. See how to reduce your bounce rate.

Spam traps

Spamhaus describes trap hits as evidence of poor list collection and management, and names purchased, rented and harvested lists as their most common source. It also notes that mailboxes left inactive for more than 12 months can be turned into traps. Spam traps explained covers the kinds and how they enter a list.

Engagement

Yahoo says mail to people who do not read it, or who report it, harms your reputation, and suggests reconfirming inactive subscribers. Spamhaus lists clicks, opens and purchases among the engagement signals receivers measure. Google suggests unsubscribing people who do not open your mail, but says it does not track opens itself and that a low open rate is not necessarily a deliverability signal.

Steady volume

Google warns that sudden spikes can trigger rate limits or a drop in reputation, and asks for a steady sending rate rather than bursts. Spamhaus says bursty volume looks like an infected host. Yahoo asks you to keep the frequency people signed up for, so a weekly list does not suddenly become daily. New IPs and domains have no history at all, which is why they need warm-up.

How to see your reputation

• Google Postmaster Tools shows the spam rate Gmail users report, authentication, encryption, delivery errors and a compliance status for your domain. Google's notice on the old interface says the domain and IP reputation dashboards are being retired, because reputation is hard to act on and changes show up late. See the Postmaster Tools guide.
• Microsoft SNDS shows data per IP address you are responsible for, including a complaint rate (complaints divided by message recipients) and a filter result color: green when under 10% of messages got a spam verdict, yellow between 10% and 90%, red above 90% (SNDS FAQ). Its Junk Mail Reporting Program sends you the messages users mark as junk. Setup is in Microsoft SNDS and JMRP.
• Feedback loops at Yahoo and other providers send you each complaint so you can remove the person; Yahoo wants one active for every DKIM domain. See email feedback loops.
• Blocklists. Spamhaus's IP and Domain Reputation Checker looks up IPv4 and IPv6 addresses and domains, and explains why a listing exists and what to fix before you ask for removal. More in email blocklists.
• Your bounce codes. A reputation problem usually appears first as deferrals and rejections: Gmail's 421 4.7.28 rate limit, its 550 5.7.1 for very low reputation, or Microsoft's 5.7.606 IP ban.

What hurts it

• Mailing people who did not sign up. Google says they may mark you as spam, and asks you never to buy addresses from other companies. Spamhaus's sender guidelines go further: send bulk mail only to addresses whose owners confirmed them, and keep a dated record of each consent (double opt-in).
• Letting inactive addresses pile up until they turn into hard bounces or recycled traps.
• Making unsubscribing hard. Google says honoring unsubscribes within 48 hours protects your sending reputation; see one-click unsubscribe.
• Weak infrastructure. Spamhaus asks for reverse DNS on every sending IP that resolves to a full host name and back to the same IP, not a generic name of the hosting provider, and for a real HELO name rather than a placeholder; Microsoft names compromised machines, open relays and dynamic or residential IPs. See reverse DNS.
• Other senders under your name. Google warns that spam from affiliates affects your brand, and that test phishing messages sent from your own domain can hurt its reputation.

How to rebuild it

1. Find the stream and the source. Check which domain, IP and campaign the complaints and bounces come from. Spamhaus advises tracing the list source that brought in trap addresses and removing that source, rather than hunting single traps.
2. Stop the damage. Remove complainers reported through feedback loops, suppress hard bounces, and fix any failing authentication or DNS record.
3. Send less, to your most engaged recipients first. Spamhaus recommends measured batches to a carefully chosen engaged group, raising volume only on the results of each send. Google asks you to lower volume until bounces and deferrals drop, then increase slowly.
4. Request delisting only after the fix. Spamhaus wants to know how the problem was solved, takes SBL removal requests only from the responsible ISP, and never charges for removal (Spamhaus Blocklist).
5. Give it time. Spamhaus says improvement is not instant and that a reputation is much easier to damage than to repair; it also does not accept requests to reset one. At Gmail, a bulk sender above a 0.3% spam rate regains eligibility for mitigation only after seven days in a row below it.

Verifying the list helps with the bounce side: it removes addresses that would hard-bounce today and flags known traps and complainers with the action remove. It does not replace consent. Spamhaus says validation tools cannot clean a list of traps, and no check can find every trap, so the source of your addresses matters more.

Questions

Does a new IP address or domain give me a fresh start?

Not really. A new IP or domain has no history, so it has to be warmed up before it can carry full volume, and Yahoo says a properly authenticated domain carries its reputation across IPs. If the old list caused the problem, it will cause it again on new infrastructure.

How long does recovery take?

No provider gives a schedule. Google's compliance status uses a rolling average and asks you to recheck after seven days, and Spamhaus says repair is much slower than damage. Judge progress by the trend over several weeks of clean sending rather than by a single good day.

Is there one reputation score I can check?

No provider publishes a single score. Google is retiring its Domain and IP Reputation dashboards and replacing the Reputation dashboard with a new version. Read several signals together: spam rate, bounce codes, SNDS colors and blocklist status.

Try it

Check a few addresses with the free email checker, or clean a whole list with bulk email verification before you send to it again.

Related

• Glossary: sender reputation.
• Bounce code dictionary: what each deferral and rejection means.

Related guides

• How to use Google Postmaster Tools
• Spam traps explained
• Email blocklists explained
• Email warm-up for new IPs and domains
• Microsoft SNDS and JMRP explained
• All guides

Sources

• Google: Email sender guidelines: per-domain and per-IP tracking, shared IPs, stream separation, volume, bounces, list practices.
• Google: Email sender guidelines FAQ: spam rate thresholds, mitigation eligibility, unsubscribe timing.
• Google: Postmaster Tools dashboards: compliance status rolling average.
• Google: Learn about the deprecation of the old Postmaster Tools interface: retirement of the reputation dashboards.
• Yahoo: Sender best practices: IP and DKIM domain reputation, mail streams, spam rate, bounces, engagement, frequency.
• Microsoft: Outlook.com postmaster troubleshooting: filter factors, complaints, practices that hurt reputation.
• Microsoft: SNDS FAQ: complaint rate and filter result colors.
• Spamhaus: How does email reputation work? (February 2022): domain vs IP reputation, signals, rebuilding.
• Spamhaus: Sender guidelines: bounce rate, traps, permission, reputation resets.
• Spamhaus: Spamhaus Blocklist (SBL): fixing the cause before removal, no fees.
• Spamhaus: IP and Domain Reputation Checker: what the checker looks up.

How we wrote this: drafted by the email-validation.org team with the help of AI writing tools, from our product documentation and the sources linked in the text.