The 10 reasons emails go to spam
1. SPF, DKIM, or DMARC is misconfigured. Modern filters check authentication first. If any of the three records fails or returns a soft-fail, your message arrives flagged before content is even scored. A surprising number of “deliverability problems” turn out to be a typo in a TXT record. Run a free Email Auth Checker to verify all three in one pass.
2. Your sending domain has no reputation history. A brand-new domain emailing strangers in volume gets treated as suspicious by default. There's no behaviour history for Gmail or Outlook to weigh, so they err on the side of caution and quarantine. The fix is warming the domain for 21+ days before any cold outreach.
3. You're sending from a shared IP with bad neighbours. If you're on a shared sending IP (common with budget ESPs), one spammy sender on the same IP can downgrade everyone. Check your IP against Spamhaus, SORBS, and Barracuda to see if any are flagged.
4. Your domain is on a blocklist. Spamhaus DBL, URIBL, SURBL, and Barracuda BRBL maintain real-time blocklists. Hitting any of them tanks placement immediately. The free Blacklist Checker scans 21 of the major lists in one pass.
5. Your content patterns trigger filters. Specific patterns receivers downgrade: ALL CAPS subject lines, too many exclamation points, spam-trigger words (“FREE”, “limited time”, “act now”), excessive emojis, and very high link-to-text ratios. None are deal-breakers alone, but they compound. Run your template through the Email Template Analyser to score it.
6. You're sending too much too fast. A new domain sending 200 emails on day one looks identical to a botnet. Volume needs to ramp gradually — which is exactly what warming is for.
7. Your recipient list has bad addresses. High bounce rates (over 5%) signal a poorly maintained list, which signals spammer to a filter. Verify your list with NeverBounce, ZeroBounce, or MillionVerifier before sending.
8. You have a low engagement rate. Filters score recent recipient behaviour. If your last 1,000 emails were opened by 8% and replied to by 0.5%, the next batch starts at a disadvantage. Engagement compounds in both directions.
9. You're using a public link shortener. bit.ly, tinyurl, and t.co are heavily abused by spam, so filters downrank any URL using them. Use a custom subdomain you own. (See: Do links impact email deliverability?)
10. Your sending pattern looks automated. Sending every email at the same time of day, from the same mailbox, with the same template structure, produces an engagement footprint that reads as automation. Real humans don't do that. This is where persona-based warming makes a measurable difference — varied behavioural patterns across mailboxes produce engagement that filters treat as legitimate.
How to diagnose which one is hitting you
Run these checks in order. Stop at the first failure.
- Authentication. Use a free Auth Checker that runs SPF (including the 10-lookup limit), DKIM (probing common selectors), DMARC parsing, MX, and BIMI. Fix any failures before going further.
- Blocklist status. If your domain is on a major list, deliverability won't improve until you delist. Submit removal requests at each list's site.
- Inbox placement test. Send a test email to seed addresses you control on Gmail, Outlook, and Yahoo. Check where it lands. Spam everywhere is reputation. Spam on Outlook only is M365-specific.
- Content scan. Run your template through a spam-score checker. Score under 5 is safe; over 7 needs revisiting.
- Engagement audit. Pull your last 30 days of sends and check open/reply rates by mailbox. If one mailbox is dragging the average, it has reputation damage specifically.
How to fix each one
| Problem | Fix | Time |
|---|---|---|
| Auth failure | Fix DNS records, wait 24h, re-test | 1 day |
| New domain, no reputation | Warm for 21 days before cold outreach | 3 weeks |
| Bad shared IP | Move to dedicated IP or different provider | 2 days |
| On a blocklist | Submit delist request, fix root cause | 3–14 days |
| Content triggers | Rewrite subject + body, retest | 1 hour |
| Volume too high | Cut by 70%, ramp back gradually | 2 weeks |
| Bad list | Verify list, remove bounces | 1 day |
| Low engagement | Tighter targeting + warming alongside | Ongoing |
| Shortener URLs | Switch to your own subdomain | 1 day |
| Automated pattern | Vary timing, mailbox, content via personas | Ongoing |
When the only fix is warming
If you've worked through the list and your authentication is clean, you're not on a blocklist, your content is fine, and you're still landing in spam — the problem is reputation, and the only fix is time plus engagement signals. That's the gap persona-based warming is designed to close. By generating opens, replies, link clicks, and spam rescues on your domain at a realistic rate for 21+ days, a warming engine builds the behaviour history filters need to start trusting you.
It's the slowest fix on the list, but for a cold or burned domain, it's the only one that works.
Frequently asked questions about emails going to spam
Why are my emails going to spam in Gmail specifically?
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Gmail's filter (the Gemini-powered scoring layer) weighs sender behaviour heavily. If your domain has low or no reputation with Google specifically, you'll hit spam in Gmail even when Outlook and Yahoo place you in the inbox. The fix is warming through Google Workspace inboxes specifically, which builds Gmail-specific behaviour history.
Why did my emails start going to spam suddenly?
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Three usual culprits: a complaint spike from a recent send, a sudden volume jump (filters detect deviation from your baseline), or a new blocklist entry. Check Google Postmaster Tools if you have it set up, and review your most recent campaign data for unusual bounce or unsubscribe rates.
How long does it take to fix emails going to spam?
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Authentication fixes apply within 24 hours of DNS propagation. Blocklist delistings take 3–14 days. Reputation repair through warming takes 3–4 weeks of consistent positive engagement signals. The most common mistake is rushing the warming step and burning the domain again.
Will marking my own emails as 'not spam' fix this?
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It helps slightly, but only for that recipient. Filters score across the broader population. The real fix is generating enough positive engagement across many recipients that the filter updates its model of your domain. That's what spam rescue at scale (via a warming engine) produces.
Should I switch sending domains if my current one is in spam?
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Only as a last resort. Burning a domain and starting fresh costs you 3 weeks of warming and any existing reputation. Always try to fix the current domain first via the diagnostic checklist (authentication, blocklist, content, then warming).
Can a warmup tool fix emails going to spam?
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Yes, when the underlying problem is reputation. A warmup tool generates the engagement signals (opens, replies, spam rescues, link clicks) that move reputation upward over time. It cannot fix authentication issues, blocklist entries, or content problems — those need to be resolved first before warming becomes effective.
What's the difference between Promotions tab and spam?
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Promotions is Gmail's 'we'll show this but quietly' classification. Spam is 'we don't trust this enough to show by default.' Both reduce open rates, but spam is much harder to recover from. Landing in Promotions usually means your content reads as marketing; landing in spam usually means your reputation or authentication is weak.
Why does my email go to spam on Outlook but not Gmail?
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Microsoft 365 and Outlook.com run a different filtering system from Gmail, with their own per-domain reputation models. A domain can have strong Gmail reputation and weak Microsoft reputation simultaneously. The fix is warming specifically through Microsoft 365 mailboxes to build Microsoft-side behaviour history.