Email Sender Reputation: How to Check and Fix It in 2026

TL;DR

• Email sender reputation is how much Gmail, Yahoo, and Outlook trust your sending domain and IP. It decides inbox, spam folder, or outright rejection.
• Domain reputation follows you everywhere. IP reputation belongs to whoever owns the server, which is Google or Microsoft if you send from Workspace or Microsoft 365.
• Check it with Google Postmaster Tools (compliance status and spam rate), Microsoft SNDS (only if you own the IPs), blocklist lookups, your own bounce codes, and a placement test.
• Google is retiring the Domain and IP Reputation dashboards in Postmaster Tools. Compliance status and spam rate are the signals to watch now.
• Keep Gmail spam complaints under 0.1% (never 0.3%) and hard bounces under 2%.
• To fix a damaged domain: pause, find the cause, fix authentication, re-verify the list, delist, then re-warm at 10 to 20% of your old volume. Retire the domain if it has not recovered after six weeks.

What Is Email Sender Reputation?

Email sender reputation is a trust score that mailbox providers assign to your sending domain and IP addresses based on how recipients react to your mail. A strong reputation gets you into the inbox; a weak one gets you filtered to spam, throttled, or rejected.

No provider publishes the score itself. Gmail, Yahoo, and Microsoft each build their own internal view from your complaint rate, bounce rate, authentication results, sending patterns, spam trap hits, and blocklist status.

This guide is for founders, SDRs, and RevOps teams running cold outbound. It covers how domain and IP reputation differ, how to check both with the tools that still work in 2026, and a step-by-step recovery plan for a cold email domain that has started landing in spam.

Most guides on this topic were written for newsletter senders. Cold email has less margin for error: no opt-in, no brand recognition, and complaint rates that climb fast when targeting is loose.

Domain vs IP Sender Reputation

Sender reputation lives at two levels: the domain in your From address and DKIM signature, and the IP address of the server that hands your mail to the recipient. Providers score both, then combine them with message-level signals.

Domain Reputation

Domain reputation is tied to the domains that authenticate your mail: the From domain, the DKIM signing domain, and the SPF return-path domain. It also extends to domains inside the email body, including your link and tracking domains.

It is portable. Move from one sequencer to another, or from shared to dedicated IPs, and your domain's history comes with you.

That is why cold email teams send from secondary domains and keep the primary domain for customer and team mail. A burned secondary domain is a replaceable asset; a burned primary domain hits invoices, support replies, and password resets.

IP Reputation

IP reputation is tied to the server that sends your mail. It is built from the combined behavior of every sender on that IP.

On a shared IP pool, other senders' bad habits can drag you down. On a dedicated IP, you own the whole history, which only works at steady volume; Mailgun, for example, recommends at least 100,000 emails a month before moving to a dedicated IP.

Which One Matters for Cold Email

If you send cold email from Google Workspace or Microsoft 365 inboxes, domain reputation is the one you control. Google and Microsoft own those sending IPs, manage their reputation at a scale no single sender can affect, and do not give you access to IP-level data.

IP reputation becomes your problem only when you send through your own mail server, a dedicated IP from an email service provider, or a cheap SMTP reseller with a shared pool.

The Rules Gmail, Yahoo, and Outlook Enforce

Gmail, Yahoo, and Outlook.com now enforce written sender requirements, and failing them damages sender reputation faster than anything else. The thresholds below come from Google's email sender guidelines, Yahoo's sender best practices, and Microsoft's Outlook rules for high-volume senders.

Two details catch cold emailers out. Per Google's sender guidelines FAQ, a domain that crosses the bulk threshold once is treated as a bulk sender permanently, and Gmail started ramping up enforcement against non-compliant traffic in November 2025.

Microsoft originally said non-compliant high-volume mail would go to Junk from May 5, 2025, then updated its announcement to reject it outright with a 550 5.7.515 Access denied error. If you see that code, our guide to 550 permanent failure errors walks through the DNS fixes.

How to Check Your Email Sender Reputation

To check email sender reputation, combine provider dashboards (Google Postmaster Tools, Microsoft SNDS, Yahoo's feedback loop) with blocklist lookups and your own bounce and placement data. No single tool gives the full picture, and cold email volumes are often too low for the provider dashboards to show anything.

Most senders skip this step entirely. A 2024 Mailgun and Sinch survey found that nearly 70% of senders do not use Google Postmaster Tools, Microsoft SNDS, or Yahoo's sender tools at all.

Google Postmaster Tools (and the v2 Changes)

Google Postmaster Tools is the only first-party window into how Gmail sees your domain. Verify each sending domain with a DNS TXT record and data starts flowing once volume is high enough.

The v2 interface, which Google documents here, includes these dashboards:

• Compliance status. Whether your domain meets Gmail's sender requirements, with DMARC and unsubscribe checks applied to bulk senders.
• Spam rate. The share of DKIM-authenticated mail that recipients marked as spam, calculated daily.
• Authentication. The percent of your mail passing SPF, DKIM, and DMARC.
• Encryption. The percent of mail sent over TLS.
• Delivery errors. The percent of authenticated mail Gmail rejected or temporarily deferred, with the reason.

The big change is reputation. Google's deprecation notice for the old Postmaster Tools says the Domain and IP Reputation dashboards will be retired, and the v2 API covers every v1 feature except domain and IP reputation.

Google has postponed shutting down the legacy interface, so you may still see the old High, Medium, Low, and Bad labels for now. Google's stated reasons: reputation was hard to act on, slow to reflect changes, and only one of many deliverability factors.

The practical takeaway: stop waiting for a reputation label. Watch the spam rate trend, the compliance status, and the delivery errors dashboard instead.

One limit matters for cold email. Postmaster Tools only shows data once a domain sends enough Gmail volume, and a secondary domain sending 100 cold emails a day across three inboxes often shows nothing at all.

Microsoft SNDS

Microsoft Smart Network Data Services (SNDS) shows how Outlook.com sees individual sending IPs, including traffic data and Junk Email Reporting Program complaint reports. SNDS now runs on a new Microsoft portal, and network access expires 10 months after approval unless you re-attest ownership.

SNDS only works for IP owners. If you send from Microsoft 365 or Google Workspace, you do not own the IPs and cannot register them, so SNDS is useful only for teams running dedicated IPs or their own servers.

Without SNDS, your Outlook signal is your bounce log. Watch for 550 5.7.515 (authentication) and 451 4.7.650 deferrals, which Outlook.com uses when it temporarily rate-limits a server because of IP reputation.

Yahoo Complaint Feedback Loop

Yahoo's Complaint Feedback Loop sends you a copy of each message a Yahoo or AOL user reports as spam. It is keyed to your DKIM signing domain, so it works even on shared IPs.

Cold email to Yahoo and AOL addresses is rare in B2B, but the loop is free and tells you exactly which campaign and which copy generated complaints.

Blocklist Checks

Blocklists (also called blacklists) are lists of domains and IPs that spam filters consult before accepting mail. A listing on a major one can push you to spam across many providers at once.

Check three things, not just your sending domain: the sending domain, your link or tracking domain, and any dedicated IPs.

• Spamhaus. The most influential list. Its Domain Block List (DBL) covers domains in senders and links, and its ZEN lists cover IPs. Free lookups and removal requests run through check.spamhaus.org.
• MXToolbox Blacklist Check. Checks a domain or IP against dozens of lists in one pass. Good for a quick sweep; prioritize Spamhaus, Barracuda, and SpamCop hits over obscure lists.
• Barracuda Reputation Lookup. Many corporate gateways use Barracuda, so a listing here hurts B2B cold email in particular.

Shared tracking domains from sequencers are a common source of listings you did not cause. Our custom tracking domain setup guide shows how to move links onto a domain only you send from.

Sender Score and Talos

Validity Sender Score rates sending IPs from 0 to 100, and Cisco Talos rates IPs and domains as Good, Neutral, or Poor.

Both are useful second opinions for dedicated IPs. For Workspace and Microsoft 365 senders they mostly score Google's and Microsoft's shared infrastructure, not you, so treat a Talos domain rating as the more relevant of the two.

Bounce Codes and Placement Tests

Your own sending data is often the earliest warning, especially for low-volume cold domains that never show up in Postmaster Tools. Two sources matter most.

SMTP bounce codes: Gmail's SMTP error reference spells out reputation-related rejections. Watch for these:

• 421 4.7.28: Gmail has detected an unusual rate of email from you.
• 550 5.7.28: an unusual rate of unsolicited email from your IP.
• 550 5.7.1: the message is likely unsolicited, or the sending IP has very low reputation.
• 550 5.7.26: the sender is unauthenticated, which points to SPF, DKIM, or DMARC rather than reputation.

Inbox placement tests: a seed-list test sends one campaign email to test inboxes at Gmail, Outlook, and Yahoo and reports where it landed. Our email deliverability test guide covers the tools, and a SpamAssassin score check catches content issues that corporate gateways still penalize.

Sender Reputation Health Check

Use this scorecard weekly for every cold email domain. The spam rate thresholds come from Google and Yahoo; the rest are working rules of thumb used by outbound teams, not published provider limits.

What Damages Sender Reputation

Sender reputation is damaged mostly by recipient behavior and list quality, not by individual words in your copy. These are the common causes for cold email, roughly in order of impact.

1. Spam complaints. Every Report spam click is a direct negative signal. Loose targeting is the root cause far more often than bad copy.
2. Hard bounces. A bounce rate above 2% tells providers you are mailing a bought, scraped, or stale list. One unverified upload can do it.
3. Spam traps. Recycled and pristine trap addresses hide in old and scraped lists. A trap hit can trigger a blocklist listing even with low complaints.
4. Volume spikes. Jumping from 20 to 200 sends a day on a new domain looks like a compromised account. Reputation is built on consistent, gradual volume.
5. Broken or misaligned authentication. SPF, DKIM, or DMARC failures now trigger rejections at Gmail and Outlook.com, and failed mail cannot build reputation.
6. Low engagement. Deletes without reading and no replies add up. Providers read silence from thousands of recipients as a sign the mail is unwanted.
7. Shared or blocklisted link domains. Sequencer tracking domains and URL shorteners shared with spammers pull your domain reputation down with theirs.
8. Bad IP neighbors. Only relevant on cheap shared SMTP pools, where one abusive sender can get the whole IP range blocked.

Diagnose the Problem by Symptom

Match what you see to the likely cause before you change anything. Fixing copy when the real problem is a blocklist wastes weeks.

If the problem is the Promotions tab rather than spam, see how to avoid the Gmail Promotions tab; that is a formatting fix, not a reputation one.

How to Fix a Damaged Sender Reputation

To fix email sender reputation on a cold email domain, stop the damage first, then fix the cause, clean the list, and rebuild trust with low, consistent volume. The order matters: re-warming a domain that still has an authentication problem or a dirty list just burns it again.

Step 1: Pause Cold Sends Immediately

Pause every active campaign on the affected domain the day you spot the problem. Each extra day of complaints or bounces deepens the hole.

Leave warmup running at low volume if the domain is not on a major blocklist. Warmup traffic keeps a baseline of positive engagement while you investigate.

Step 2: Find the Cause

Work through the checks from the how to check section in this order:

1. Hard bounce rate for each campaign over the last 14 days. Above 2% points straight at the list.
2. Postmaster Tools spam rate, compliance status, and delivery errors.
3. Blocklist lookups for the sending domain, tracking domain, and any dedicated IPs.
4. Raw headers of a sent email to confirm SPF, DKIM, and DMARC pass and align with the From domain.
5. Recent changes: a new list source, a volume jump, a new template, or a new link.

Step 3: Fix Authentication and Tracking

Make sure each sending domain has one SPF record under the 10-DNS-lookup limit, a 2048-bit DKIM key, and a DMARC record at p=none or stricter with reporting turned on. Our Gmail DKIM setup guide covers the Workspace steps.

Then remove shared tracking. Turn open and click tracking off, or move it to a custom tracking domain you own, and strip URL shorteners from every template.

If you are on a cheap shared SMTP pool, this is also the moment to move to better infrastructure. Our best email hosting for cold email comparison covers the options.

Step 4: Re-Verify the List

Re-verify every contact still queued in a sequence before a single email goes out again. Hard bounces and spam traps are the most common reasons cold domains get burned, and both come from the list.

• Remove every address that verifies as invalid.
• Move catch-all and unknown results into a separate segment and send to it later, in small batches, once the domain has recovered.
• Drop role addresses like info@ and sales@, which draw complaints and rarely reply.
• Suppress anyone who complained, unsubscribed, or asked not to be contacted.
• Treat any address verified more than 30 days ago as unverified.

SyncGTM verifies each email through a waterfall across multiple verification providers at 0.1 credits per address, returning valid, invalid, risky, or unknown with catch-all and role flags. Re-checking 5,000 queued contacts costs 500 credits; plan sizes are on the SyncGTM pricing page.

The same check is available to AI agents through the SyncGTM MCP server, so a list-building agent can verify contacts before it hands them to your sequencer. For a broader look at verification tools, see our free email verifier roundup.

Step 5: Request Blocklist Removal

Request removal only after the cause is fixed. Spamhaus and other major lists will relist a domain quickly if the same behavior continues, and repeat listings take longer to clear.

For Spamhaus, use the lookup at check.spamhaus.org, which shows the listing reason and a removal path. Barracuda has a removal request form linked from its lookup page, and many smaller lists expire listings automatically once the bad traffic stops.

Step 6: Re-Warm and Ramp Slowly

Restart cold sends at 10 to 20% of the domain's previous volume. If an inbox was sending 40 cold emails a day, restart it at 5 to 8.

Raise volume by about 20% a week while hard bounces stay under 2% and placement tests stay clean. Send to your best-verified, best-fit segment first, and write for replies, because replies are the strongest positive signal you can earn.

Our email domain warmup guide and warmup schedule comparison have day-by-day ramps, and the Gmail warmup guide covers Workspace inboxes specifically.

Step 7: Know When to Retire a Domain

Sometimes a fresh domain is cheaper than a long recovery. Retire a cold email domain when any of these is true:

• It is listed on Spamhaus again after a removal.
• Placement tests still land mostly in spam after four to six weeks of clean re-warming.
• The Gmail spam rate stays at or above 0.3% even at low volume.

Before you buy a replacement, fix the root cause. A new domain that inherits the same list and the same volume plan burns in weeks.

Keep spare warmed domains in rotation so a retirement does not stop outbound. Our best domain registrars for cold email guide covers bulk purchase and DNS control.

How Long Does Recovery Take?

Sender reputation recovery usually takes one to twelve weeks, depending on how much damage was done and how quickly you caught it. Providers do not publish recovery timelines, so treat these as typical ranges, not guarantees.

How to Protect Sender Reputation Going Forward

Protecting sender reputation is cheaper than repairing it. Build these habits into every campaign:

1. Send cold email only from secondary domains, never from your primary domain.
2. Warm every new domain and inbox for 2 to 4 weeks before cold sends.
3. Cap each inbox at 30 to 50 sends a day, follow-ups included, and scale by adding inboxes.
4. Verify every list within 30 days of sending and keep hard bounces under 2%.
5. Target tightly. Relevant emails draw replies; loose lists draw complaints.
6. Write short plain-text emails with zero or one link and no tracking pixel on the first touch.
7. Include a clear opt-out line and honor it immediately.
8. Check Postmaster Tools, blocklists, and a placement test every week, not after a problem.

For the full prevention playbook, read how to avoid spam filters with cold email.

Conclusion

Email sender reputation is the gate every cold email has to pass, and for Workspace and Microsoft 365 senders, the domain is the part you control. Check it weekly with Postmaster Tools, blocklist lookups, bounce codes, and placement tests, because the reputation labels you used to rely on are going away.

When it drops, pause, find the cause, fix authentication, re-verify the list, delist, and re-warm slowly. Most domains come back; the ones that do not should be retired before they drag the rest of your outbound down.

Ready to fix the list side? Try SyncGTM free and verify every contact before your next campaign goes out.