Your emails go to spam for one of eight reasons: failing authentication, a weak sender reputation, spammy content, risky links or tracking domains, too much volume too fast, a list full of bad addresses, low engagement, or a blacklist listing. Most cases trace back to one or two of these, and each can be tested in minutes. Start with a free placement test such as Warmy's free email deliverability test, which needs no sign-up, then use the checklist below; our Warmy review explains the paid side of that tool.
Some tool links here are affiliate links (disclosure). Nerdy Joe is an affiliate of Warmy and MailReach. Nerdy Joe is a certified Apollo.io Managed Services Partner and a PlusVibe Certified Silver Partner.
We did not run hands-on tests of any tool for this guide. Provider rules come from Google, Yahoo and Microsoft's own pages, tool facts come from each vendor's site as of November 2026, and sources are listed at the end.
Quick diagnosis: which cause is it?
Match your symptom to the likely cause, then jump to that section.
| Symptom | Most likely cause | First test |
|---|---|---|
| Rejected with a 5.7.x error, or spam at every provider | Authentication | DNS lookup plus a header check on a real sent email |
| Spam at one provider only, Gmail most often | Reputation or engagement | Postmaster Tools spam rate; per-provider placement test |
| Plain email inboxes, campaign email does not | Content or links | Send both versions to a seed list |
| Started after you raised daily sends | Volume | Compare send logs to the date placement dropped |
| Many bounces, then spam | List quality | Bounce rate in your sending tool |
| Started overnight with no changes on your side | Blacklist | Blacklist check on domain, IP and linked domains |
| New domain or mailbox | Reputation (no history yet) | Warmup status; placement test |
If you are unsure, run the full sequence in our email deliverability test guide, which checks these in order.
What Google, Yahoo and Microsoft require
These rules come from each provider's official page. Failing them is the most common hard reason mail goes to spam or gets rejected.
| Requirement | Google (Gmail) | Yahoo | Microsoft (Outlook.com) |
|---|---|---|---|
| Who it applies to | All senders to Gmail accounts; stricter rules at 5,000+ a day | All senders; stricter rules for bulk senders | Domains sending more than 5,000 a day to Outlook.com consumer addresses |
| Authentication | SPF or DKIM for all; SPF, DKIM and DMARC for bulk | SPF or DKIM at minimum; SPF, DKIM and DMARC (p=none or stronger) for bulk | SPF and DKIM must pass; DMARC at least p=none |
| Alignment | From domain aligned with SPF or DKIM (bulk) | From domain aligned (bulk) | DMARC aligned with SPF or DKIM |
| DNS and transport | Valid forward and reverse DNS; TLS | Valid forward and reverse DNS | Not listed in the post |
| Spam rate | Below 0.3%; keep below 0.10% | Below 0.3% | No number published |
| Unsubscribe | One-click for marketing and subscribed mail (bulk) | One-click; honor within 2 days (bulk) | Visible unsubscribe recommended |
| Enforcement | Requirements apply since February 1, 2024 | Not stated in the items we read | Rejection with 550 5.7.515 since May 5, 2025 |
Google's page also says "Don't send messages to people who didn't sign up to get messages from you." Meeting the technical rules does not make unwanted mail welcome.
Cause 1: Authentication fails
SPF, DKIM and DMARC prove the mail comes from your domain. A missing record, two SPF records, a DKIM key that was never published, or a DMARC record pointing at the wrong domain will send mail to spam or get it rejected outright.
How to test. Look up your SPF, DKIM and DMARC records, then send a real email to a Gmail address and open "Show original" to see whether SPF, DKIM and DMARC say PASS. Placement tools such as Warmy's free test and MailReach's spam test also report authentication results from a real send.
How to fix. - Keep one SPF record that includes every service that sends for you. - Publish DKIM for each sending service; Google asks for a 1024-bit key at minimum and recommends 2048. - Publish DMARC at p=none to start, aligned with SPF or DKIM. - Warmy has free SPF, DKIM and DMARC generators; its DMARC generator suggests p=none for about 2 to 4 weeks before moving to quarantine and then reject.
Every sending domain needs this, not only the main one. Our cold email infrastructure guide covers the full setup.
Cause 2: Sender reputation is weak or new
Providers judge your domain and IP by history. A brand new domain has none, and a domain that drew complaints has a bad one. Microsoft's sender support page says new IPs "typically don't have any reputation built up" and are more likely to see deliverability issues.
How to test. Verify your domain in Google Postmaster Tools and watch the spam rate for mail to personal Gmail accounts. Google is retiring the Domain and IP Reputation dashboards in the new version of Postmaster Tools, so spam rate and delivery errors are the signals to watch. For Outlook, Microsoft's SNDS shows data for IPs you control.
How to fix. - Slow down. Google says to increase volume slowly and start with engaged users. - Warm new mailboxes and domains before campaigns. Our email warmup guide covers timelines and a sample ramp. - Pause campaigns on a damaged domain while you repair it.
Warmup tools such as Warmy automate the ramp with network mailboxes. Google's sender guidelines recommend increasing volume slowly to engaged recipients and do not mention warmup tools, and Gmail's program policies prohibit automating Gmail in ways that mislead or deceive users.
Warmy says its warmup emails stay inside its own network and its terms make customers responsible for following provider policies; MailReach says Google has not banned warmup. Google has not published a position on warmup networks specifically, so treat automated warmup as a practice Google neither endorses nor explicitly names.
Warmup also does not change real recipient complaints, which is what Google's spam rate measures.
Cause 3: Content looks like spam
Filters read subject lines, body text, images and HTML. Heavy templates, image-only emails, all-caps urgency and aggressive sales phrasing all add risk, especially on a domain without a strong reputation.
How to test. - Paste your subject and body into our free spam word checker and rewrite flagged phrases. - Warmy's free template checker tests for "spammy words or phrases" in plain text or HTML. - Send a plain two-sentence version and your real version to the same seed list. If only the real one lands in spam, the cause is content or links.
How to fix. Write cold email as short plain text, with one clear ask and no attachments. Keep images out of first-touch emails. Content scores are rule-based estimates, since no provider publishes its filter, so confirm with a placement test.
Cause 4: Links and tracking domains
Every link is a domain the filter checks. A URL shortener, a link to a blacklisted site, too many links, or open and click tracking on a shared tracking domain can all pull an otherwise clean email into spam.
How to test. - Run each linked domain through a blacklist checker. - Send one version with tracking and links and one without to a seed list, and compare. - Check which tracking domain your sending tool uses by hovering a link in a test email.
How to fix. - Use full links to your own domain; avoid shorteners. - Keep links to one or two per email, or none in the first touch. - Set up a custom tracking domain that matches your sending domain, as MailReach recommends, or turn tracking off.
Cause 5: Volume rose too fast
A mailbox that sent 20 emails yesterday and 300 today looks like a compromised account. Google tells senders to send at a consistent rate and avoid spikes, such as doubling volume.
How to test. Compare your sending tool's daily volume per mailbox with the date placement dropped. Look for new mailboxes added straight into full campaigns.
How to fix. - Cut volume back to the last level that inboxed, then raise it in small steps. - Spread volume across more mailboxes and domains instead of pushing one harder. MailReach recommends no more than 100 cold emails a day per address, and says 80 or fewer is better. - If messages bounce or defer, Google's advice is to reduce volume until the error rate drops, then increase slowly.
Cause 6: List quality and bounces
Sending to invalid, old or purchased addresses produces hard bounces, and some old addresses become spam traps. High bounce rates tell providers you do not know your recipients. Google's page says "Don't purchase email addresses from other companies."
How to test. Check your bounce rate per campaign and per mailbox. Sequencers draw the line in different places: Smartlead's blog calls under 2% good, lemlist says keep it under 3%, and Instantly's default auto-pause triggers above 5%. Mailbox providers publish spam-rate thresholds, not bounce thresholds.
How to fix. - Verify every list before sending. Our roundup of the best email verification tools compares options, and Warmy also includes email verification in its plans. - Remove hard bounces immediately and stop retrying addresses that soft bounce repeatedly. - Never send to bought lists.
Our guide to email bounce rate covers how it is calculated, hard vs soft bounces and the full set of thresholds.
Cause 7: Low engagement and complaints
Providers watch what real recipients do. Deleting without reading, never replying, and pressing "Report spam" all push future mail toward spam. Microsoft calls the junk complaint rate one of the principal factors that drives down reputation, and advises against sending to recipients who never read or reply.
How to test. Watch the Gmail spam rate in Postmaster Tools, your reply rate, and unsubscribe and complaint counts in your sending tool. A falling reply rate on the same offer is an early warning.
How to fix. - Tighten targeting so each email is relevant to the person who gets it. - Make opting out easy; Yahoo asks bulk senders to honor unsubscribes within 2 days. - Cut follow-ups. MailReach recommends at most 2 follow-ups, at least 3 days apart. - Keep Google's spam rate below 0.10%. No warmup or seed engagement offsets complaints from real recipients.
Cause 8: Blacklist listing
A blacklist (or blocklist) is a public list of domains and IPs linked to spam. A listing on your domain, your sending IP or a domain you link to can send mail to spam at receivers that consult that list.
How to test. Warmy's free blacklist checker queries 25 lists at once for your domain and every IP it resolves to, including Spamhaus, Barracuda, SpamCop and SURBL, with no sign-up. Check linked domains too.
How to fix. Find and fix the cause first: a compromised account, a bad list, a spike. Then use the list operator's removal process.
No tool can remove a listing for you, and Warmy's checker page itself advises fixing the root cause before requesting removal. Paid Warmy plans add daily blacklist monitoring with alerts, per Warmy.
How to test where your email lands
Every fix above should be confirmed with a placement test. You send the real email to a seed list of mailboxes at Gmail, Outlook, Yahoo and business providers, and the tool reports where each copy landed.
- Warmy's free deliverability test reports Inbox, Promotions, Spam and Unreceived by provider, plus sending IP blacklist status, with no sign-up, and flags results when less than 80% reach the inbox.
- MailReach's free spam test allows up to 3 tests per 24 hours with no card, per MailReach, and adds content and authentication checks.
Use the real sending tool and domain, test a plain control email alongside, change one thing at a time, and re-test. Our inbox placement test guide covers seed lists and reading results by provider in full.
Spam diagnosis checklist
- [ ] SPF, DKIM and DMARC all pass on a real sent email
- [ ] Only one SPF record per domain
- [ ] Postmaster Tools verified; Gmail spam rate below 0.10%
- [ ] Domain, sending IP and every linked domain clear of blacklists
- [ ] Copy passed a spam word check; plain text, no attachments
- [ ] No shorteners; custom tracking domain or tracking off
- [ ] Daily volume per mailbox steady, with no recent spikes
- [ ] List verified; bounce rate low and hard bounces removed
- [ ] Follow-ups limited and unsubscribes honored within 2 days
- [ ] New mailboxes warmed before campaigns
- [ ] Placement test run after every fix
Rather not build the list yourself?
Most spam problems in cold email start with the list and the sending setup. Nerdy Joe is owned by Agency Growth Partners (AGP), and AGP builds verified lists and runs outbound for agencies.
If you would rather hand that off, book a call with David.
Bottom line
When emails go to spam, test before you guess: authentication first, then blacklists, list quality, volume, links, content and engagement. Fix one cause at a time and confirm each change with a placement test, and once mail is landing again, compare monitoring options in our roundup of email deliverability tools.
To check placement right now, run Warmy's free deliverability test. If you are considering Warmy's paid warmup and monitoring, the full Warmy review covers pricing, strengths and limits.
Sources
- Gmail Help: Email sender guidelines
- Gmail Help: Gmail Program Policies
- Gmail Help: Postmaster Tools changes
- Google Workspace Admin Help: Postmaster Tools
- Yahoo Sender Hub: Sender best practices
- Microsoft Tech Community: Outlook's new requirements for high-volume senders
- Microsoft Support: Sender support in Outlook.com
- Microsoft SNDS
- Warmy: Free email deliverability test
- Warmy: Free blacklist checker
- Warmy: Free template checker
- Warmy: Free DMARC generator
- Warmy: Email verification
- Warmy: Reputation Repair
- Warmy: Terms of Service
- Warmy Help: The inbox deliverability checker
- Warmy blog: GMass alternative
- MailReach: Email spam test
- MailReach blog: Email warmup solutions, in-house vs third-party services
- MailReach Help: How to get the highest reputation score
- Smartlead blog: Cold email bounce rate
- lemlist Help: Understanding and reducing bounces
- Instantly Help: High bounce auto pause
Frequently asked questions
Why are my emails suddenly going to spam?
A sudden change usually has a sudden cause: a volume spike, a new link or tracking domain, a bad list with many bounces, a DNS change that broke SPF or DKIM, or a new blacklist listing. Check what changed in the last few days first, then run an authentication check and a placement test.
Why do my emails go to spam in Gmail but not Outlook?
Each provider runs its own filters and keeps its own view of your reputation. Gmail weighs real recipient spam reports heavily, so a high spam rate in Postmaster Tools can hurt Gmail placement while Outlook still delivers, and the reverse also happens.
How do I stop my emails from going to spam?
Fix authentication first (SPF, DKIM, DMARC), then clean your list, slow your volume, simplify your links and copy, and send only to people likely to want the email. Test each change with a seed placement test before scaling back up.
Does landing in the Promotions tab count as spam?
No. Promotions is a Gmail inbox tab, not the spam folder. Warmy's placement reports count Promotions as delivered to the inbox, though a plain one-to-one email landing there may still be read less.
Can a spam word in my email send it to spam?
It can contribute, but one word rarely decides placement on its own. Providers do not publish their filters, and content usually tips a message into spam only when reputation or authentication is already weak.
How long does it take to get out of spam?
It depends on the cause. A broken DNS record can be fixed in a day, while reputation damage takes longer; Warmy's Reputation Repair page says Gmail domain reputation often takes several weeks to recover.