Table of Contents
- What Is a Spam Filter and How Does It Work?
-
Why Do Emails Go to Spam? (16 Common Reasons)
- 1. Lack of Email Authentication (SPF, DKIM, DMARC)
- 2. Poor Sender IP Reputation
- 3. Bad Domain Reputation
- 4. High Spam Complaint Rates
- 5. Low Subscriber Engagement
- 6. Dirty Email Lists
- 7. Suspicious Links or Shorteners
- 8. Poor Email Content
- 9. Missing or Broken Reply-To Address
- 10. No Plain-Text Version
- 11. Large or Suspicious Attachments
- 12. Sloppy HTML Coding
- 13. Inconsistent Sending Patterns
- 14. Form Abuse or Non-Consented Subscribers
- 15. Non-Compliance with Anti-Spam Laws
- 16. Email Tracking Pixels
- How to Check If Your Emails Are Going to Spam
-
12 Proven Ways to Stop Emails Going to Spam
- 1. Authenticate Your Emails Properly
- 2. Choose a Reputable ESP
- 3. Warm Up Your Sending IP
- 4. Use Double Opt-In
- 5. Clean Your Email List Regularly
- 6. Personalize Your Emails
- 7. Avoid Spam Trigger Words
- 8. Optimize Image-to-Text Ratio
- 9. Make Unsubscribing Easy
- 10. Monitor Sender Reputation
- 11. Comply with Anti-Spam Laws
- 12. Test Before Sending
- Want a Shortcut to Stop Emails Going to Spam? (Skip all These 12 Strategies)
- FAQs About Emails Going to Spam
Emails go to spam. Three words that can kill your marketing campaigns instantly. I’ve sent over 6.2 million emails, and when we started Outbound Masters, I watched our carefully crafted emails go to spam instead of reaching prospects.
It was like burning money. So I got obsessed with fixing it.
After months of testing, I figured out exactly why emails go to spam and what actually works to land in the inbox. This journey led me to create Sparkle, our email verification tool.
Here’s what nobody tells you about spam filters: they’re smart but predictable. Once you understand their patterns, you can work with them instead of against them.
In this post, I’ll share the real reasons your legitimate emails get flagged as spam and the practical fixes that will change your deliverability game for good.
Let’s get into it.
What Is a Spam Filter and How Does It Work?
At its core, a spam filter is just an algorithm that email providers like Gmail, Yahoo, and Outlook use to protect their users from unwanted or potentially harmful emails. Think of it as a bouncer at the door of your prospect’s inbox. When your prospects ask, “Is my email spam?” about messages they receive, these filters have already made that decision.
How Spam Filters Actually Work to Determine If Emails Go to Spam
The process determining why emails go to spam is more complex than most marketers realize:
Understanding how to avoid emails going to spam isn’t just for tech nerds or email specialists. If you’re sending any kind of marketing emails and don’t know why your emails go to spam, this directly impacts your bottom line.
For every email going to spam, you’re losing potential customers, appointments, and revenue. Learning how to prevent emails going to spam is essential to your marketing success.
Why Do Emails Go to Spam? (16 Common Reasons)
After analyzing thousands of campaigns and investigating why my emails go to spam, I’ve identified these 16 deliverability killers that explain why emails go to spam:
1. Lack of Email Authentication (SPF, DKIM, DMARC)
These three acronyms might sound technical, but they’re essentially digital ID cards for your emails. Without proper authentication, you’re sending emails with no identification, and spam filters don’t like that.
Think of it this way: you wouldn’t let a stranger into your house without ID, would you? Email providers feel the same way about their users’ inboxes.
2. Poor Sender IP Reputation
Your IP address is like your email’s credit score. Send spammy content or generate complaints, and that score tanks. With a bad IP reputation, even your legitimate emails get caught in the crossfire.
I’ve seen new clients come to us with IP reputations so bad that 80% of their emails were going straight to spam, regardless of content.
3. Bad Domain Reputation
Similarly, your domain name carries its own reputation. New domains are automatically suspicious to spam filters, and domains with a history of spam complaints might as well have a “reject me” sign attached.
4. High Spam Complaint Rates
When recipients click “mark as spam,” it’s like they’re reporting you to the email police. If your complaint rate exceeds about 0.1% (that’s just 1 complaint per 1,000 emails), you’re in dangerous territory.
5. Low Subscriber Engagement
Spam filters look at how people interact with your emails. Low open rates, quick deletions without reading, and ignored emails all signal to providers that your content isn’t wanted.
In one campaign, we increased deliverability by just removing subscribers who hadn’t opened our emails in 90 days.
6. Dirty Email Lists
Sending to inactive addresses, spam traps, or bought lists is like walking into a minefield. One hit and your reputation is blown.
7. Suspicious Links or Shorteners
Link shorteners (like bit.ly) and suspicious URLs raise red flags. Spam filters know that malicious senders use these to hide dangerous destinations.
8. Poor Email Content
Overusing words like “free,” “guarantee,” “no risk,” excessive punctuation (!!!), or ALL CAPS will trigger spam filters faster than you can say “limited time offer.”
9. Missing or Broken Reply-To Address
A functional reply-to address signals you’re a legitimate sender open to communication. Without one, spam filters get suspicious.
10. No Plain-Text Version
Some spam filters flag HTML-only emails as potential spam. Always include a plain-text alternative to your fancy HTML emails.
11. Large or Suspicious Attachments
Sending attachments in marketing emails is generally a bad idea. Large files or suspicious file types (like .exe) will almost certainly trigger spam filters.
12. Sloppy HTML Coding
Broken code, excessive inline CSS, or mismatched tags signal unprofessionalism and can trigger technical spam filters.
13. Inconsistent Sending Patterns
Spam filters love consistency. If you normally send 200 emails weekly, then suddenly blast 20,000, alarm bells ring.
14. Form Abuse or Non-Consented Subscribers
Bots filling out your forms or adding non-verified emails to your list create deliverability nightmares.
15. Non-Compliance with Anti-Spam Laws
Legal requirements like CAN-SPAM and GDPR aren’t just legal issues—they’re deliverability issues too. Missing unsubscribe links or required contact information will land you in spam folders.
16. Email Tracking Pixels
Those tiny, invisible tracking pixels that tell you when someone opens your email? They’re increasingly flagged by modern spam filters. These 1×1 pixel images load from external servers and can trigger spam or privacy filters, especially with privacy-focused email providers like Apple Mail or ProtonMail.
In our testing, simply turning off open rate tracking increased inbox placement with certain providers. While tracking data is valuable, it’s worthless if your email never reaches the inbox in the first place.
How to Check If Your Emails Are Going to Spam
Before you can fix the problem of emails going to spam, you need to know if you have one. Here’s exactly how to check if your emails are going to spam:
✅ Test with Spam Checkers
Tools like MailTester, GlockApps, or Litmus analyze your emails before you send them and identify potential spam triggers that explain why your emails go to spam.
When we started using spam checkers to understand why my emails go to spam, we found issues we’d never even considered—like invisible content in our templates that was triggering filters.
✅ Send Test Emails
Create accounts with major providers (Gmail, Yahoo, Outlook) and send test emails to see where they land. Check both the inbox and spam folders to verify if your email going to spam is happening across different providers.
✅ Monitor Analytics
Your email service provider’s dashboard reveals crucial metrics that indicate if your emails go to spam:
- Low open rates (under 15-20%)
- High bounce rates (over 2%)
- Rising spam complaints
These are all warning signs that your emails are going to spam instead of the inbox.
✅ Seed List Testing
Create a “seed list” of email addresses across different providers to check if your emails are going to spam. Send your campaign to this list first and track where the emails land. This gives you direct evidence about whether emails go to spam and which providers are filtering your messages.
12 Proven Ways to Stop Emails Going to Spam
Now for the fixes that will transform your deliverability and prevent emails going to spam:
1. Authenticate Your Emails Properly
Setting up SPF, DKIM, and DMARC isn’t optional anymore—it’s essential. Here’s a technical breakdown of each:
a) SPF (Sender Policy Framework):
- Purpose: Specifies which mail servers are authorized to send email on behalf of your domain
- Implementation: Add a TXT record to your DNS with this syntax:
v=spf1 include:_spf.google.com include:_spf.mailchimp.com ip4:123.45.67.89 ~all
|
- Validation: Check with dig TXT yourdomain.com from the command line
b) DKIM (DomainKeys Identified Mail):
- Purpose: Creates a cryptographic signature that verifies email authenticity
- Implementation:
- Generate a public/private key pair (2048-bit RSA recommended)
- Add the public key as a TXT record at selector._domainkey.yourdomain.com
- Configure your mail server to sign outgoing emails with the private key
- Example TXT Record:
v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA1Kd87/UeJjenpabgbFwh9GBqe… |
- Technical Impact: Prevents email spoofing and header tampering
c) DMARC (Domain-based Message Authentication, Reporting & Conformance):
- Purpose: Ties together SPF and DKIM, provides reporting, and failure handling
- Implementation Levels:
Monitoring (start here):
v=DMARC1; p=none; rua=mailto:dm***********@yo********.com” data-original-string=”W1fsF8I0gGtQEYPTm/4FjA==558yvrqlUOf9VEy2KbmtpbPckIKUSo+SZk1UScGwg2DR7c1cMCfuKl8cRQdBMWdOw16H2wqPXMtQccSYMmd7A6sFGTTE6/VV6sVO0c7RuABO3s=” title=”This contact has been encoded by Anti-Spam by CleanTalk. Click to decode. To finish the decoding make sure that JavaScript is enabled in your browser.; pct=100 |
Quarantine (intermediate):
v=DMARC1; p=quarantine; rua=mailto:dm***********@yo********.com” data-original-string=”YdD9NBlwW/CH4AKqrDLBcQ==558Y/tOXXX94x0nWg8mM7i25axUMo3fNDhEGOC6tRsRSkpsi8SnwpTiu0iOv8cbos4O/f8UgNO7RSJHIT+b2ih52Nk8WNW01ZnFShaI5zaIDE0=” title=”This contact has been encoded by Anti-Spam by CleanTalk. Click to decode. To finish the decoding make sure that JavaScript is enabled in your browser.; pct=25 |
Reject (advanced):
v=DMARC1; p=reject; rua=mailto:dm***********@yo********.com” data-original-string=”K9chA0t9z4WliKNL/2GfQQ==558Yr48GE1EsRAM5kBWRt6IOtGidBCI4qYq8TMF1rkETxj2uffrJ89yXyBsf71cpaJObR9pCpKr8S1KfrR67W20CrJm8Oy2MFMfZEujqzRAc/s=” title=”This contact has been encoded by Anti-Spam by CleanTalk. Click to decode. To finish the decoding make sure that JavaScript is enabled in your browser.; pct=100 |
Parameters Explained:
- p=: Policy (none, quarantine, reject)
- rua=: Where aggregate reports are sent
- pct=: Percentage of messages subject to filtering
- adkim=s: Strict DKIM alignment (optional)
- aspf=s: Strict SPF alignment (optional)
Implementation Timeline: Allow 2-4 weeks at each policy level to analyze reports
2. Choose a Reputable ESP
Your Email Service Provider is your partner in deliverability. Choose established providers like Mailchimp, SendGrid, or Constant Contact, which have relationships with inbox providers and robust anti-spam practices.
3. Warm Up Your Sending IP
New IP addresses need to build trust gradually through a process called IP warming. This is crucial because mailbox providers track sending patterns and reputation at the IP level.
Technical Aspects of IP Warming:
- Starting Volume: Begin with 50-100 emails/day to your most engaged subscribers
- Increment Rate: Increase by 100% every 2-3 days until you reach normal volume
- Monitoring Metrics: Track these during warming:
- Inbox placement rate (target: >95%)
- Bounce rate (keep below 2%)
- Spam complaint rate (keep below 0.1%)
- Open rate (target: >20%)
Sample 30-Day IP Warming Schedule:
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Day | Daily Volume | Target Audience | Marketing Focus | Performance Indicators |
1-2 | 50-100 | Top 10% most engaged subscribers | High-value content only | Open rate >30%, Complaint rate <0.1% |
3-5 | 200-300 | Top 25% most engaged subscribers | Engagement-focused content | Click rate >5%, Bounce rate <1% |
6-9 | 500-800 | Top 50% most engaged subscribers | Mix of content types | Maintain previous metrics, Monitor domain reputation |
10-13 | 1,000-1,200 | 75% of engaged subscribers | Regular campaign content | Inbox placement >90%, Unsubscribe rate <0.2% |
14-18 | 1,500-2,000 | All engaged subscribers | Full campaign mix | No deliverability warnings, Stable open rates |
19-24 | 2,500-3,500 | All engaged + recent inactive (60 days) | Re-engagement focused | Monitor carefully for complaint spikes |
25-30 | 4,000-5,000+ | Full list with gradual increases | Complete marketing calendar | Establish new normal metrics baseline |
Reputation Monitoring Tools:
- Google Postmaster Tools: https://postmaster.google.com/
- Microsoft SNDS: https://sendersupport.olc.protection.outlook.com/snds/
- ReturnPath Sender Score: https://senderscore.org/
Using this precise IP warming schedule increased our new client’s deliverability from 54% to 91% in just three weeks. The technical reason? We established consistent sending patterns that aligned with mailbox provider algorithms designed to detect legitimate email traffic.
4. Use Double Opt-In
Make subscribers confirm their email address before adding them to your list. This simple step dramatically reduces spam complaints and bounces.
Our tests show double opt-in lists typically have 30% fewer deliverability issues than single opt-in.
5. Clean Your Email List Regularly
Remove subscribers who haven’t engaged in 3-6 months. Yes, your list will shrink, but your deliverability (and ROI) will improve.
Here’s a simple cleaning process:
- Identify subscribers with no opens/clicks in 3+ months
- Send a re-engagement campaign
- Remove those who don’t respond
6. Personalize Your Emails
Segmented, personalized emails generate more engagement, which improves your sender reputation. Use subscribers’ names, reference their past interactions, and send content relevant to their interests.
7. Avoid Spam Trigger Words
Some words and phrases are notorious spam triggers:
- “Free”
- “Guarantee”
- “No risk”
- “Limited time”
- “Act now”
Use these sparingly and never stack them in subject lines or opening paragraphs.
8. Optimize Image-to-Text Ratio
Aim for about 60% text and 40% images. Image-heavy emails with minimal text scream “spam” to filters.
9. Make Unsubscribing Easy
Counter-intuitive but true: easy unsubscribes mean fewer spam complaints. Place your unsubscribe link where it’s easily found and make it one-click simple.
10. Monitor Sender Reputation
Tools like SenderScore and Barracuda let you track your IP and domain reputation. Check weekly and address issues promptly.
11. Comply with Anti-Spam Laws
CAN-SPAM, GDPR, and other regulations aren’t just legal matters—they’re deliverability boosters. Always include:
- Physical mailing address
- Clear identification of your business
- Honest subject lines
- Visible unsubscribe option
12. Test Before Sending
A/B test subject lines, content, and sending times with a small segment before sending to your entire list. Use what performs best for the full campaign.
Want a Shortcut to Stop Emails Going to Spam? (Skip all These 12 Strategies)
Let’s be honest—implementing all 12 strategies to avoid emails going to spam takes time and technical know-how. It took me years to perfect these techniques through trial and error of figuring out why my emails go to spam.
That’s exactly why I built Sparkle.io. After seeing so many businesses struggling with the same “why do my emails go to spam” questions I faced, I created a tool that handles the technical parts for you.
With a 99% delivery rate, Sparkle takes care of:
- Email verification before sending to prevent emails going to spam
- Authentication monitoring to stop emails going to spam
- Reputation management to avoid emails going to spam
- Content scanning for spam triggers that answer “why do emails go to spam”
It’s like having an email deliverability expert on your team 24/7, making sure your messages land where they belong—in the inbox, not the spam folder. If you’re tired of seeing your emails go to spam, Sparkle is your answer.
FAQs About Emails Going to Spam
Do blocked emails go to spam?
No. Blocked emails are rejected completely, while spam-filtered emails are delivered to the spam folder. If your emails are blocked, you’ll typically receive a bounce notification. This is an important distinction when diagnosing why emails go to spam versus when they’re blocked entirely.
Do BCC emails go to spam?
Not automatically, but using BCC for mass emails can trigger spam filters. Many people ask “do BCC emails go to spam?” because they notice lower deliverability when using BCC. Modern email marketing should use proper email service providers instead of BCC to prevent emails going to spam.
How do I know if my email is marked as spam?
To check if your emails are going to spam, look for low open rates, feedback from subscribers, and send test emails to seed accounts. These are your best indicators when you’re wondering “is my email spam?” Tools like GlockApps can also provide direct spam folder placement data to verify if your emails go to spam.
Can I recover from a bad sender reputation?
Yes, but it takes time and consistent good practices. If you’ve determined that poor reputation is why your emails go to spam, start with a new IP if possible, implement authentication, clean your list, and gradually rebuild your sending reputation with quality content to engaged subscribers. This is key to stop emails going to spam long-term.
What's the difference between spam and junk folders?
Technically, they’re the same thing with different names. Some email clients use “Junk” (like Outlook) while others use “Spam” (like Gmail), but the filtering mechanisms that determine why emails go to spam are similar. Whether your messages are in “spam” or “junk,” the problem and solutions for stopping emails going to spam are the same.
