Why Emails Go to Spam (Real Causes + Fixes)

Why this happens

Even with properly configured domains and mailboxes, cold emails can still land in spam.

Modern ESPs like Gmail, Outlook, and Yahoo evaluate many signals before deciding whether an email belongs in inbox or spam.

Spam placement is usually caused by a combination of:

• Mailbox reputation

• Domain reputation

• Sending behavior

• Email content

• Recipient engagement

• Technical setup

In most cases, it is not caused by a single issue.

Most Common Reasons Emails Go to Spam

1. Mailboxes are not properly warmed up

New mailboxes have no reputation.

If you start campaigns too aggressively before warming up, ESPs may flag your emails as suspicious.

Fix

• Warm up mailboxes for 2-3 weeks before scaling

• Keep warm-up enabled continuously

• Increase sending volume gradually

Pre-warmed mailboxes still require ongoing warm-up activity.

2. Your email copy triggers spam filters

This is one of the most common causes.

Even with healthy infrastructure, repetitive or overly salesy copy can trigger spam filters.

Common causes

• Repetitive messaging

• Too many links

• Aggressive sales language

• Overused signatures

• Lack of personalization

• Heavy formatting or images

Fix

• Use personalization and spintax

• Keep emails short and natural

• Reduce links and tracking

• Rotate signatures occasionally

• Write conversational emails

3. Links inside the email are blacklisted

If your email contains blacklisted links, ESPs may instantly send the message to spam.

Fix

• Remove links and test again

• Avoid URL shorteners

• Use custom tracking domains

• Check domains using blacklist tools

Useful tools:

• MXToolbox Blacklist Check

• Mailmeteor Spam Checker

• Mail Tester

4. Sending volume increased too quickly

Sudden spikes in sending volume are a major red flag.

Fix

Scale slowly over time.

Example:

• Week 1: 10-20/day

• Week 2: 20-40/day

• Week 3: 40-60/day

Avoid aggressive scaling on new domains.

5. Low engagement signals

If recipients ignore, delete, or mark your emails as spam, your reputation declines.

Fix

• Improve targeting

• Personalize emails deeply

• Focus on reply rates instead of volume

6. Poor technical setup

Missing or incorrect DNS records can hurt deliverability.

Important records

• SPF

• DKIM

• DMARC

Fix

• Verify all DNS records

• Use secondary domains for outreach

• Avoid too many mailboxes per domain

7. Sending to lookalike domains

Sending test emails between similar domains can trigger phishing protection.

Example

If your domain is:

• companyhq.com

Avoid testing with:

• company-hq.com

• companymailhq.com

Fix

Use unrelated domains for testing.

8. Poor lead quality or invalid contacts

High bounce rates damage sender reputation quickly.

Fix

• Validate contacts before sending

• Remove invalid leads regularly

• Avoid outdated databases

A healthy bounce rate should generally stay below 3%.

9. Recipient-side spam filters

Some companies use aggressive internal spam filters.

This is common with:

• Enterprise companies

• Government organizations

• Financial institutions

Fix

• Simplify content

• Reduce links

• Avoid attachments

• Use plain-text emails

How to Diagnose Spam Issues

Step 1: Send manual test emails

Login directly into the mailbox and send emails manually.

If manual emails land in inbox but campaign emails go to spam, the issue may be related to:

• Email copy

• Tracking links

• Sending platform settings

• Sending IPs

Step 2: Remove content gradually

Test your sequence by removing elements one by one.

For example:

• Remove links

• Remove signature

• Remove images

• Simplify wording

• Reduce formatting

This helps identify the exact trigger.

Step 3: Use spam testing tools

Recommended tools:

• Mail Tester

• Mailmeteor Spam Checker

• MXToolbox Blacklists

These tools help identify:

• Blacklisted domains

• Missing DNS records

• Spam-triggering copy

• Reputation problems

Best Practices to Stay Out of Spam

Infrastructure

• Use secondary domains

• Configure SPF, DKIM, and DMARC correctly

• Limit mailboxes per domain

Sending behavior

• Warm up continuously

• Scale slowly

• Avoid volume spikes

• Keep bounce rates low

Email copy

• Personalize emails

• Use spintax

• Keep emails short

• Reduce links

Lead quality

• Validate contacts

• Target relevant prospects

• Avoid outdated lead lists

Important Note About Pre-Warmed Mailboxes

Pre-warmed mailboxes complete the initial warm-up process, but inbox placement can still be affected by:

• Email copy

• Links

• Sending behavior

• Lead quality

• Recipient spam filters

If warm-up emails land in inbox but campaign emails go to spam, the issue is usually related to campaign content or targeting rather than mailbox infrastructure itself.

Key Takeaways

Spam placement is rarely caused by a single issue.

Deliverability depends on the combination of:

• Healthy infrastructure

• Proper warm-up

• Good sending behavior

• High-quality lead lists

• Human-sounding email copy

The best approach is to test incrementally and optimize one variable at a time.

Small improvements in copy, targeting, and sending habits can significantly improve inbox placement over time.