10 Common Reasons Emails Go to Spam (2025 Guide to Inbox Placement)

You hit send on an important email campaign. You expect clicks, replies, maybe even sales. But instead, your carefully written message ends up buried in the spam folder. It’s frustrating—and unfortunately, incredibly common.

In fact, according to Validity’s Email Deliverability Benchmark Report (2024), nearly 20% of marketing emails never reach the inbox. That’s one in every five emails wasted before it even has a chance. For businesses that rely on email for revenue, this can mean thousands of dollars lost every month.

The problem is that mailbox providers like Gmail, Outlook, and Yahoo have built powerful spam filters to protect users. But those same filters sometimes punish legitimate senders who make common mistakes.

In this 2025 guide, we’ll cover the 10 most common reasons emails land in spam, with practical examples and actionable steps to keep your messages where they belong—the inbox.

1. Lack of Email Authentication (SPF, DKIM, DMARC)

Think of authentication like airport security. Without valid ID, you won’t get on the plane. Similarly, without authentication, your emails won’t make it to the inbox.

• SPF (Sender Policy Framework): verifies which servers can send emails for your domain.

• DKIM (DomainKeys Identified Mail): attaches a digital signature proving authenticity.

• DMARC: tells providers how to handle suspicious emails and prevents spoofing.

According to Google Postmaster data (2024), domains without proper SPF/DKIM setup had a 35% lower inbox rate compared to authenticated domains.

Without these, Gmail and Outlook treat you as a potential imposter.

Real Example:

A SaaS company sending from a brand-new domain forgot to add DKIM. Their open rates dropped by 70% in two weeks. After setting up SPF + DKIM + DMARC, inbox placement bounced back within days.

Checklist:

• Use tools like MXToolbox or Google Postmaster Tools.

• Ensure SPF includes all legitimate sending servers.

• Align “From” domain with authenticated domain.

2. Sending From a New or Unwarmed Domain

Mailbox providers treat brand-new domains with suspicion. If you send thousands of emails on day one, it looks like spam.

Real Example:

A startup launched with a new domain and sent 50,000 cold emails in one week. Gmail throttled their messages, and nearly 90% went to spam.

How to Fix It:

• Start with 20–50 emails/day.

• Gradually double sending volume.

• Use warm-up networks like Zharik AutoWarmup.

• Avoid campaigns from a domain younger than 2 weeks.

3. Poor Sender Reputation

Mailbox providers give each sender an invisible reputation score. Complaints, high bounce rates, or blacklists tank that score.

Validity’s 2024 study found that senders with complaint rates over 0.3% saw inbox placement drop below 60%.

Why It Matters:

• A reputation below threshold = automatic spam.

• Complaint rates above 0.1% (1 complaint per 1,000 emails) raise red flags.

Checklist:

• Monitor blacklists (Spamhaus, Barracuda, etc.).

• Keep complaint rates low by targeting only engaged users.

• Track domain health using Postmaster Tools.

4. Buying or Using Dirty Email Lists

Purchased lists are poison. They contain spam traps, inactive addresses, and users who never asked for your emails.

Real Example:

An e-commerce store bought a “100,000 verified emails” list. Within days, their domain got blacklisted, and even transactional emails (order confirmations) went to spam.

How to Fix It:

• Build organic lists with double opt-in.

• Validate regularly to remove dead addresses.

• Never use data brokers—your reputation is worth more.

5. High Volume Sending Too Quickly

HubSpot reports that brands using purchased lists see average unsubscribe rates 3× higher than organic lists.

Example Scenario:

You usually send 1,000 emails a day. One week, you send 50,000. ISPs see an unnatural spike and trigger filters.

 Tips:

• Spread campaigns across multiple days.

• Segment lists and throttle sends.

• Keep volume increases gradual.

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6. Misleading or Spammy Subject Lines

Subject lines are the first filter. Words like “FREE!!!” or deceptive clickbait tank trust.

Litmus data (2024): subject lines with all caps saw a 26% drop in inbox placement.

Data Point:

According to Litmus (2024), subject lines with excessive caps or exclamation marks had 26% lower inbox placement.

 Do’s:

• Keep subject lines under 60 characters.

• Use personalization naturally.

• Be honest (don’t say “Your invoice” if it’s a promotion).

 Don’ts:

• ALL CAPS SUBJECTS.

• Multiple $$$ signs.

• Overused buzzwords like “Act now,” “Limited offer,” etc.

7. Poor Email Content & Formatting

Even if your subject is fine, messy content triggers filters.

Common Triggers:

• Too many images vs. text.

• Broken HTML or missing plain-text version.

• Overuse of shortened URLs.

Fix:

• Keep text-to-image ratio around 60:40.

• Include a plain-text version.

• Use branded short links.

8. Ignoring Engagement Metrics

ISPs track what recipients do: open, click, reply, delete.

Low engagement = bad signals → spam.

Example:

If less than 10% open rate persists, Gmail assumes your emails aren’t wanted.

 Solutions:

• Segment users by activity.

• Run re-engagement campaigns (“We miss you!”).

• Remove inactive subscribers every 90 days.

9. Failing to Provide Unsubscribe Options

No unsubscribe = frustrated users → spam complaints.

Legal Risk:

• GDPR fines can reach €20M or 4% of annual revenue.

• CAN-SPAM fines up to $50,000 per violation.

Best Practice:

• Always include a visible unsubscribe link.

• Offer frequency options (weekly, monthly).

• Honor requests immediately.

10. Overusing Cold Email Without Personalization

Cold outreach works—but only if personalized. Bulk cold campaigns often end in spam.

Real Example:

A recruiter sent 5,000 identical cold emails. Open rates: 3%. Spam complaints: through the roof. After switching to personalized templates, open rates rose to 38%.

Fix:

• Use recipient name, company, or recent activity.

• Limit volume per day.

• Test different templates.

How to Keep Emails Out of Spam in 2025

Avoiding spam isn’t about tricking filters—it’s about proving you’re a reliable sender.

5-Step Strategy:

1. Authenticate everything (SPF, DKIM, DMARC).

2. Warm up gradually (never blast from zero).

3. Keep lists clean (validate and remove inactive users).

4. Engage your audience (personalization, relevant content).

5. Monitor performance (open rates, complaint rates, blacklists).

💡 Want to make it easier? Zharik AutoWarmup and Email Validation automate much of this process, saving you time and keeping your reputation healthy.

FAQ

Why are my emails going to spam in Gmail?

Usually due to missing authentication, poor reputation, or low engagement. Gmail’s AI filters in 2025 are stricter than ever.

How do I stop my emails from going to spam in Outlook?

Authenticate your domain, keep bounce rates low, and follow Microsoft’s sender guidelines.

What words trigger spam filters in 2025?

Excessive “FREE,” “Act Now,” “100% Guarantee,” too many emojis, or misleading phrases.

Does email warm-up prevent spam?

Yes. Warm-up builds trust gradually by simulating real engagement, especially important for new domains.

How long does email warm-up take?

Typically 2–4 weeks for a new domain, depending on volume and engagement.

What is a good open rate in 2025?

Across industries, 18–25% is average. Anything lower signals problems with deliverability or relevance.

What’s the difference between delivery and deliverability?

Delivery = the email didn’t bounce. Deliverability = the email actually reached the inbox, not spam.

Conclusion

In 2025, the inbox is crowded—and mailbox providers are more protective than ever. But if you avoid these 10 mistakes and follow best practices, your chances of hitting the inbox increase dramatically.

Remember: email deliverability isn’t about gaming the system. It’s about building trust with both ISPs and your audience. Do that, and your campaigns will not only reach the inbox but also drive the engagement and revenue you’re aiming for.

 Ready to boost your deliverability? Try Zharik AutoWarmup and Email Validation today.