If your emails keep landing in the spam folder, it is rarely random. Mailbox providers like Gmail, Yahoo, and Microsoft use surprisingly predictable signals to decide where your message ends up. Fix the signals and you fix the placement. Here are the eleven causes we see most often.
1. You skipped email verification
This is the big one. If your list contains a meaningful percentage of invalid or disposable addresses, your bounce rate spikes, your sender reputation tanks, and Gmail starts routing you to spam on principle. Fix: clean every list before sending. MailoClean bulk verifier handles a million emails per hour.
2. SPF, DKIM, or DMARC is missing or broken
These three DNS records are the email equivalent of a passport. Gmail and Yahoo started requiring all three for bulk senders in early 2024. If any one is missing or misconfigured, you are going to spam regardless of content. Run your sending domain through any DMARC checker. If you see "fail" anywhere, fix it before your next campaign.
3. Your sending domain is too new
Brand-new domains have zero reputation. Mailbox providers treat them as untrusted by default. Warm up the domain by sending small, high-engagement batches for the first two to four weeks before scaling up.
4. The "From" address looks like spam
noreply@, donotreply@, info@, sales@ all read as low-trust. Use a real person's name in the From line: jane@acme.com beats noreply@acme.com every single time.
5. The subject line is screaming
ALL CAPS, multiple exclamation marks, words like "FREE!!!" or "ACT NOW". You know the type. The spam filters know them too. Write subject lines a human friend would actually send you.
6. Image-to-text ratio is out of whack
Beautiful all-image emails look professional and trigger spam filters. Aim for at least 60% text. If your designer hands you a Photoshop comp with no actual words, push back.
7. Too many links
One CTA, two at most. Five or more links in a short email reads as link farm to most filters.
8. URL shorteners
bit.ly, tinyurl, t.co. Spammers love shorteners because they hide destinations. So do filters. Use your own branded short domain or full URLs.
9. Your engagement rate is collapsing
Mailbox providers watch what subscribers do with your past emails. If opens and clicks are dropping over time, future emails get demoted. Re-engage or remove inactive subscribers every 90 days.
10. You bought or scraped the list
Just do not. Purchased lists almost always contain spam traps, and one trap hit can put you on Spamhaus for months. Build your list organically or do not build it.
11. Spam complaints over 0.1%
Every time someone hits "Report spam", Gmail logs it. Above 0.1% complaint rate, you get demoted to bulk folder by default. Make unsubscribe one-click and obvious; do not hide it in 8pt gray text at the bottom.
The deliverability checklist
- Clean your list with MailoClean before every campaign.
- Confirm SPF, DKIM, DMARC all pass.
- Warm up new sending domains slowly.
- Use a real human From name and reply-to.
- Write subject lines that pass the "would my friend send this" test.
- Keep image-to-text ratio above 60% text.
- One primary CTA per email.
- Skip URL shorteners.
- Re-engage or remove inactive subscribers quarterly.
- Never buy or scrape lists.
- Make unsubscribe one-click.
FAQ
How long does it take to recover from being marked as spam?
Four to eight weeks of consistent good behaviour. Start by cleaning your list, fixing your auth records, then send only to your most engaged 20% for two weeks before slowly adding the rest back.
Will verifying my list stop emails going to spam?
It is one of the biggest factors but not the only one. Verification fixes bounce rate; the rest of the checklist fixes the other signals. Both matter.
Fix the biggest one first
If you have not verified your list this quarter, that is where to start. Upload a CSV and clean it today.