What is sender reputation, and how do you improve it?

When you send an email, the receiving mailbox provider has a split second to decide: inbox, spam folder or reject. Much of that decision rests on your sender reputation, the provider's memory of how mail from you has behaved before. This guide explains what reputation is made of, the difference between IP and domain reputation, where you can see yours, and how to repair it.

What is sender reputation?

Sender reputation is a score, or set of scores, that each mailbox provider keeps about the sources of the mail it receives. It isn't one universal number. Gmail, Outlook.com, Yahoo and corporate filters each keep their own, based on what they see.

Spamhaus puts it plainly: "Reputation systems are designed to automate spam filtering," and reputation "is composed of an unknown number of variables that ISPs or reputation providers like Spamhaus do not reveal" (Spamhaus). So nobody can show you the exact formula. What providers do publish is what they want from senders, and that tells you what feeds the score.

Reputation matters for every sender, not just marketers. A small business whose invoices land in spam has a reputation problem too. If that's you, start with why your emails are going to spam.

What's the difference between IP and domain reputation?

Providers track reputation for several identities in each message. The two that matter most:

Yahoo says "each IP and DKIM domain has a reputation, which can impact the delivery of your email" (Yahoo Sender Hub). Google's sender guidelines warn that on a shared IP, "the activity of any senders using a shared IP address affects the reputation of all senders for that shared IP address."

The balance has shifted toward domains. Spamhaus says "IP reputation is less important than the reputation of domains and content for inbox placement," partly because IPv6 makes addresses so plentiful that spammers can discard them. For the choice between your own IP and a provider's pool, see shared vs dedicated IP for email.

What affects sender reputation?

The signals below come from what Google, Yahoo, Microsoft and Spamhaus publish. Weightings are private.

Spam complaints

Complaints are the most direct signal. Google says "over time, user spam reports can lower your domain's reputation," and asks senders to keep the spam rate in Postmaster Tools "below 0.10% and avoid ever reaching a spam rate of 0.30% or higher." Yahoo's requirements for all senders say "keep your spam rate below 0.3%." Our guide to spam complaint rates explains how the rates are calculated, and feedback loops show you which messages drew complaints.

Bounces and list hygiene

Repeatedly sending to addresses that don't exist suggests a list nobody maintains. Yahoo says to "remove invalid recipients from your list promptly" and to "monitor hard and soft bounces as well as inactive recipients." Spamhaus adds that "bounce management needs to be handled quickly." See hard bounce vs soft bounce.

Spam traps

Spam traps are addresses that never asked for mail. Hitting them tells providers and blocklists that your list includes addresses nobody consented to. Our guide to spam traps covers pristine, recycled and typo traps.

Authentication and infrastructure

Authentication lets a provider attach reputation to your domain with confidence. Spamhaus notes reputation systems "do care whether or not mail is authenticated correctly." Gmail requires SPF or DKIM from everyone, and SPF, DKIM and DMARC from bulk senders; see Gmail, Yahoo and Microsoft bulk sender requirements. Sending IPs also need valid reverse DNS (PTR) records.

Engagement

Spamhaus says "the more engagement an email receives, the better deliverability gets." Yahoo recommends sending "timely and relevant email to an active and engaged audience." Mail that's consistently ignored teaches the provider that your messages aren't wanted.

Volume consistency

Google is specific: "Send email at a consistent rate," "avoid sending email in bursts," and "immediately doubling previously sent volumes suddenly could result in rate limiting or reputation drops." Spamhaus warns that "'bursty' email streams will degrade even well-established reputation." That's why new domains and IPs need warming up.

Where can you see your sender reputation?

No single dashboard shows it all. Combine these.

Google Postmaster Tools

Postmaster Tools shows Gmail's view of your domain: spam rate, authentication, encryption, delivery errors and compliance with Gmail's sender requirements. Google tells senders to "check your spam rate and your domain and IP address reputation with Postmaster Tools." Note that, at the time of writing (October 2026), Google is moving to a new version and says "the Domain and IP Reputation dashboards" will be retired and the reputation view replaced, with no firm date (Gmail Help). Spam rate is the number to watch.

Microsoft SNDS and JMRP

For mail to Outlook.com and Hotmail, Microsoft offers Smart Network Data Services (SNDS), "a free service that provides high-level insight on how users are rating the email they receive," and the Junk Mail Reporting Program (JMRP) for complaint reports (Outlook.com Postmaster). SNDS is for IPs you own; if you send through Microsoft 365, Google Workspace or a shared email service, you can't register those IPs. See our Outlook.com deliverability guide.

Blocklists

Public blocklists are the bluntest reputation signal: listed or not. Check your sending IP and domain with the Blacklist Checker. Some lists, including Spamhaus, refuse lookups through public resolvers, so confirm any doubt on the list's own site. Listings are specific; Spamhaus's CSS, for example, lists IPv4 addresses individually and IPv6 in "/64" or larger blocks (Spamhaus).

Your own mail logs and bounces

Deferrals and rejections often say why. A 421 "try again later" with a reputation note, or a 550 naming a blocklist, is the provider telling you what it thinks. Look up codes in our SMTP error code reference, and send a test message through the Deliverability Test to see authentication, reverse DNS and blocklist results in one place.

How do you repair a damaged sender reputation?

Fix the cause first. Requests for removal before that tend to fail, and the problem returns.

1. Find the source. Which IP, domain and mail stream is affected? Marketing, transactional and everyday mail can each damage a shared domain.
2. Rule out compromise. A sudden drop often means a hacked mailbox, a compromised website form or malware sending spam. Check outbound volume and signs an email account is compromised.
3. Fix authentication and DNS. SPF, DKIM and DMARC passing and aligned, and a forward-confirmed PTR on every sending IP. Run your domain through the Email Health Check and the IP through the PTR Lookup.
4. Clean the list. Remove hard bounces, long-inactive recipients and any purchased or scraped addresses. Honor unsubscribes quickly; see one-click unsubscribe.
5. Cut volume, then rebuild. Send only to your most engaged recipients at first, at a steady rate, and increase slowly as complaints and bounces stay low.
6. Request delisting from any blocklist once the cause is fixed, following each list's process. Our blocklist removal guide covers the main ones.
7. Separate streams for the future. Send marketing from a subdomain so a campaign problem doesn't hit your invoices. See separate subdomains for transactional and marketing email.

Be patient. Spamhaus warns that "it is much, much easier to drive reputation down than it is to fix a damaged one."

How do you keep a good sender reputation?

• Send only to people who asked for your mail, and make leaving easy.
• Keep complaint rates well under 0.1% in Postmaster Tools.
• Remove bounces automatically and prune inactive recipients.
• Keep SPF, DKIM and DMARC passing for every service that sends as your domain.
• Send at a steady pace; ramp up gradually for new domains, IPs or big campaigns.
• Check blocklists and Postmaster Tools on a schedule, not only when something breaks.
• Watch for DNS changes that break authentication without anyone noticing.

Next steps

• Set up Google Postmaster Tools for your sending domain today, so you have data before you need it.
• Run your sending IP through the Blacklist Checker and the PTR Lookup.
• Use the Email Health Check to confirm SPF, DKIM and DMARC.
• iBlockSpam's domain monitoring alerts you when your MX, SPF or DMARC records change, which catches the silent DNS edits that hurt authentication.

Browse more email basics guides.