A burned cold email domain rarely announces itself. There is no email from Google telling you your reputation is shot. Instead, replies dry up, bounces creep up, and by the time most teams notice, they have been mailing straight into spam for weeks. Since Gmail and Yahoo started enforcing strict sender requirements in early 2024, with Outlook following in 2025, the margin for error has kept shrinking, and in 2026 the filters are more aggressive than ever. Here are the six signs your cold email domain is in trouble, followed by the five tools we would actually use to diagnose and fix it.
Sign 1: Your Open Rates Fell Off a Cliff
Healthy B2B cold email on a warmed domain typically lands somewhere in the 25 to 45% open rate range, depending on list quality. If you were sitting at 40% and dropped to 12% without changing your list or your copy, that is not a subject line problem. A sudden, sustained drop is the single most common early symptom of reputation damage, because spam-folder emails almost never get opened.
Sign 2: Inbox Placement Is Below 80% in Seed Tests
Open rates are a proxy. Seed testing is the direct measurement: you send to a list of test inboxes across Gmail, Outlook, and Yahoo and see exactly where the message lands. Practitioners generally treat placement below 80% as a fire alarm requiring immediate action. If your seed tests show Gmail putting you in spam while Outlook still inboxes you, that also tells you which provider’s reputation system you have damaged.
Sign 3: Bounce Rates Are Creeping Past 3%
Bounces above roughly 3% signal sloppy list hygiene to every mailbox provider, and sustained high bounce rates compound the damage: each bounce further degrades the reputation that is already causing your placement problems. If your bounce rate has been climbing for two or three consecutive campaigns, the domain is absorbing damage even if opens still look acceptable.
Sign 4: Spam Complaints Above 0.1%
Google’s enforced ceiling for bulk senders is a 0.3% spam complaint rate, but waiting until you hit it is like waiting for the engine fire. Deliverability practitioners treat 0.1% as the action threshold. Complaints are the strongest negative signal a recipient can send, and cold outreach earns them fast when targeting is loose. A complaint spike on one campaign can follow your domain around for months.
Sign 5: Your Domain or IP Is on Blacklists
Blacklist appearances are a lagging indicator, meaning that by the time you show up on one, the behavior that got you listed has been running for a while. Not all lists matter equally, but appearing on major ones correlates strongly with the spam placement you are seeing. Weekly blacklist checks should be part of any outbound routine; most burned-domain post-mortems reveal the listing happened weeks before anyone looked.
Sign 6: Google Postmaster Shows Low or Bad Reputation
This is the closest thing to an official verdict. Google Postmaster Tools reports your domain reputation on a four-level scale directly from Gmail’s infrastructure, and a domain sitting at Low or Bad is, for practical purposes, burned for Gmail delivery. Recovery from Bad is slow enough that many teams find it faster to retire the domain and rebuild on a fresh secondary domain, warming it properly for three to six weeks this time.
5 Tools to Fix a Burned Cold Email Domain
Diagnosis and repair need different instruments. These five cover the full stack without redundant spend.
1. Google Postmaster Tools
Free, and non-negotiable. Postmaster gives you domain reputation, spam complaint rates, and authentication reporting straight from Gmail, which is where most of your B2B recipients live. Set it up before you need it, because it only reports on ongoing volume. Best for: knowing definitively whether Gmail considers you a spammer.
2. MxToolbox
The free tier covers blacklist lookups plus SPF, DKIM, and DMARC verification. Broken authentication is one of the most common and most fixable causes of spam placement, and since mailbox providers made authentication mandatory, a single misconfigured DNS record can sink an otherwise healthy domain. Best for: ruling out technical misconfiguration in five minutes.
3. GlockApps
GlockApps runs seed tests across a wide panel of providers, including regional ones, and shows you folder-level placement per provider, with plans from $79 per month. This is how you get the Sign 2 data above instead of guessing from open rates. Run a test before and after each fix to confirm the changes are working. Best for: measuring actual inbox placement rather than inferring it.
4. MailReach
MailReach combines warmup with placement monitoring at $19.50 per mailbox per month, generating real engagement signals that rebuild a damaged reputation gradually. Fair warning grounded in what the data shows: warmup is a supplement to good sending practices, not a substitute. It cannot outrun bad lists or spammy copy. Best for: rehabilitating a damaged domain or warming its replacement.
5. Smartlead or Instantly Built-In Warmup
If you are already sending through Smartlead or Instantly, both bundle unlimited warmup into their platforms, with Smartlead’s pool reportedly spanning over 250,000 inboxes. Most teams run two to three weeks of warmup before launching from any new mailbox, and data suggests unwarmed inboxes hit around 68% placement in week one versus 91% for warmed ones. The same reputation logic applies across channels, which is why we took a similar infrastructure-first approach in our guide to LinkedIn outreach tools that will not get your account banned. Best for: teams that want warmup without another subscription.
Rebuild It Right This Time
A burned domain is usually a symptom of a process problem: too much volume too fast, unverified lists, or a primary domain doing cold outreach it never should have touched. The 2026 playbook is boring and effective. Use secondary domains so your brand domain stays clean, warm every new mailbox for three to six weeks, verify every list, and check Postmaster and blacklists weekly. And make sure your sequencer is not the bottleneck; if you have outgrown yours, our roundup of Outreach.io alternatives covers platforms with deliverability built in. Domains are cheap. Reputations are not.