As an email marketer, whether you're sending cold emails to generate more leads or marketing newsletters to engage and retain customers, you've likely encountered email deliverability issues. Trust me, it’s inevitable.

Despite crafting the perfect email copy, setting up the correct email authentications, creating great designs, and maintaining an ideal text-to-image ratio, emails sometimes still end up in spam folders.

The good news is—you can overcome this. Email deliverability issues affect countless businesses, leading to missed opportunities and reduced engagement.

Poor deliverability doesn't just mean missed leads; it can also harm your revenue.

The root of email deliverability problems often comes down to factors like poor sender reputation, spammy content, or issues with email authentication.

In this blog, we’ll break down the most common causes of email deliverability issues and guide you on how to resolve them. Plus, we’ll show how Smartlead can help with advanced monitoring and management features, improving your deliverability and maintaining a strong connection with your audience.

We’ll primarily answer three major questions in this article:

• How to Find Email Deliverability Issues (exploring the tell-tale signs and causes)
• How to Fix Email Deliverability Problems
• How to Improve Your Sender Reputation (a key factor in email deliverability) 

How To Find Email Deliverability Issues

Email deliverability can make or break your email campaigns. 

For example, if you’re sending a cold email campaign to more than a 100 prospects or leads, but only 1% of them reach the inbox or worse, end up in spam folder, this can result in lost opportunities. 

Emails that constantly land in spam can hurt your sender reputation as well, making ESPs flag your emails as spam more often.

However, there is no accurate way to figure out where your emails went - spam or the primary folder. Some emails might bounce back due to wrong email addresses - which too, in turn can affect your sender reputation. 

So, how do you know that your email deliverability sucks? 

Well, there are some tell-tale signs that are also the causes of email deliverability issues. 

Let’s look at them below:

1. High Spam Score 

A high spam score is one of the main reasons your emails might not reach the inbox. Spam filters have grown more sophisticated, evaluating multiple factors such as your email content, structure, and sender reputation.

These spam filters are looking for specific red flags—words and phrases that may seem spammy, links to shady websites, or even unusual formatting in your emails. 

If your copy includes too many “trigger” words like “free,” “guaranteed,” or “act now,” or your email contains suspicious links, there’s a high chance your message will end up in the spam folder.

There are many spam filters out there, and they all have their own unique way of detecting unwanted emails. Here are three popular ones you should definitely keep in mind:

• SpamAssassin
  An open-source spam filter used by many hosting providers, SpamAssassin evaluates emails based on a scoring system. Emails that score too high (indicating spam-like behavior) are flagged or blocked. Learn more about SpamAssassin Score and how to fix it via this article.
• Barracuda
  A widely used commercial spam filter that employs advanced algorithms and blacklists to prevent spam emails. Barracuda is known for its aggressive filtering, especially when it comes to blocking emails from untrusted sources.
• Postini
  Acquired by Google, Postini offers powerful spam and virus filtering for Gmail and G Suite accounts. It primarily focuses on identifying phishing attempts and blocking emails with suspicious links.

So, how do you know that your emails are being marked as spam? 

First you need to figure out your spam complaint rate. Use our free spam complaints checker tool to get started. 

You can also check your email content for spam trigger words and get a spam score. Below is a result from our Spam Checker tool: 

2. Blocked by Email Providers

It’s not just spam filters that can hurt your deliverability. Major email providers like Gmail, Outlook, and Yahoo may block your emails altogether, even before they get a chance to land in any folder. The reason? 

Providers have their own systems in place to protect their users from unwanted emails.

If your sender reputation is poor—perhaps due to too many complaints, a history of low engagement, or suspected spam activity—these providers will block your emails from reaching your audience. 

Similarly, if your IP address or domain has been flagged for suspicious behavior, your emails will be blacklisted. This is why maintaining a good sender reputation is critical (more on this later), and regularly monitoring your IP health is a must.

3. Blacklisted Domain or IP Address

Nothing sinks email deliverability faster than being blacklisted. 

If your domain or IP address has been added to a blacklist, it means email providers view your messages as harmful or spammy, and they will actively prevent your emails from reaching their users.

Being blacklisted is usually a result of sending emails that are flagged as spam or having a poor sender reputation. 

It can be a serious issue that damages your overall marketing efforts. To check if you’re blacklisted, use online tools to monitor your domain and IP reputation, and if you are blacklisted, take immediate action to correct the issue. 

4. Engagement Rates

Did you know that low engagement rates also impact your deliverability? It can also be a sign that your emails are not even reaching the recipients.

Email providers track how users interact with your messages. If your emails frequently go unopened, or worse, if they’re deleted or marked as spam, email providers will take this as a sign that your emails aren’t relevant or wanted.

Low open and click rates hurt your reputation and reduce your chances of landing in the inbox over time. 

Now, when you are aware of common signs and causes of email deliverability issues, let’s move to understanding how to fix these problems. 

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How To Fix Email Deliverability Issues?

If you're experiencing poor email deliverability, there are key steps you can take to resolve these issues and get your emails back into the inbox. 

From cleaning up your email list to monitoring engagement and optimizing content, fixing deliverability issues requires a strategic approach. 

Let’s uncover each element and fixes available. 

1. Validate Your Email List

One of the most critical steps to improving email deliverability is maintaining a clean email list. 

Sending emails to invalid or outdated addresses not only wastes resources but also results in high bounce rates, which damage your sender reputation and lower your deliverability over time.

Invalid emails lead to bounces, and too many bounces signal to email providers that your list is unreliable, reducing the likelihood of future emails reaching inboxes. Regular validation ensures you're only sending emails to active, valid recipients.

How To Validate Your Email List

Use a trusted list validation tool to regularly clean your database. 

These tools scan your list, identify invalid or risky addresses (such as those from disposable email services), and remove them automatically. 

This not only helps improve deliverability but also boosts overall campaign performance, leading to higher engagement rates.

If you’re a Smartlead user, we offer an email verification service. 

Smartlead provides two options for verifying email addresses: a free version for individual checks and a paid version for bulk verification.

Free Version
For individual email checks, simply enter the address into Smartlead’s free email verification tool. This is suitable for one-off verifications but not for large lists.

Paid Version
The paid version costs $15 for 6,000 credits and allows bulk verification. To use it:

1. Create a new campaign in your Smartlead account.
2. Upload your lead list as a CSV file.
3. Launch the email verification process, which may take time depending on the file size.

4. Review the detailed report of verified emails once the process is complete.

You can download the verified leads and use them in your campaign, ensuring your emails only reach valid recipients. 

2. Improve Sender Reputation

Your sender reputation plays a huge role in whether your emails land in the inbox or get flagged as spam. A low sender reputation is one of the leading causes of poor deliverability, but improving it can significantly increase your chances of inbox placement.

Key Factors That Affect Sender Reputation

• Email Content Quality: Sending valuable, relevant, and engaging content is crucial. When recipients interact positively with your emails—such as opening them and clicking on links—it strengthens your sender reputation.
• Avoid Spammy Language: Words like “free,” “buy now,” and “guaranteed” can raise red flags for spam filters, so it’s important to avoid using language that could trigger these filters.
• Proper Authentication: Implement email authentication protocols like SPF, DKIM, and DMARC to prove to email providers that your messages are legitimate and not forged. These protocols add credibility to your emails, improving deliverability.

3. Monitor Bounce Rates and Engagement

Deliverability issues are often signaled by high bounce rates and low engagement. Monitoring these metrics closely can help you spot potential issues early and take action before they affect your entire email strategy.

Bounce Rates

High bounce rates can indicate problems with your email list. If your emails are regularly bouncing back because of invalid or inactive addresses, it’s a clear sign that your list needs cleaning. Reducing bounce rates is key to protecting your sender reputation.

Engagement Metrics

Low engagement—such as poor open rates or click-through rates—tells email providers that your content may not be relevant to your audience. This can lead to your emails being flagged as less important or even marked as spam over time.

How To Improve Engagement

• Segment Your Audience: Send targeted, relevant content to different audience segments based on their preferences and behavior.
• Personalize Your Emails: Emails that feel personal and tailored to the recipient tend to perform better. Use personalization tokens like names and past behaviors to drive engagement.
• A/B Test Your Campaigns: Test different subject lines, copy, and CTAs to see what resonates best with your audience.

4. Email Content Optimization

Crafting the right content is key to staying out of the spam folder. Spam filters closely analyze the content of your emails, looking for anything that could be deemed suspicious or spammy.

Tips for Content Optimization

• Watch Your Language: Avoid using terms that are frequently associated with spam, like “100% free,” “limited-time offer,” or “urgent.”
• Keep Your Formatting Clean: Spam filters may flag overly formatted emails (such as those with excessive bold, italics, or colored text). Keep your email layout clean and professional.
• Use a Clear Call-to-Action (CTA): Spam filters look for clarity in your emails. A clear, direct CTA improves engagement and can help keep your emails out of the spam folder.
• Balance Text and Images: Too many images can make your email look suspicious to spam filters. Ensure a good balance between text and visual elements to maintain credibility.

Test Before You Send

Before launching any campaign, run your email through deliverability and spam tests to catch any potential issues. These tests will flag problematic content or structural issues that could hurt your chances of landing in the inbox.

How To Improve Sender Reputation

Sender reputation is key to improving your email campaigns’ success and email deliverability. 

It directly affects whether your emails land in the inbox or get flagged as spam. 

Here are key strategies to enhance your sender reputation and ensure your emails are well-received.

1. Warm Up New Domains

When you start using a new domain for sending emails, it's essential to warm it up gradually. Warming up involves slowly increasing your email volume over time to build a positive reputation with ISPs and avoid triggering spam filters.

New domains can be seen as risky by email providers. If you start sending a large volume of emails immediately, it can raise red flags and lead to deliverability issues. Warming up helps establish your domain’s credibility and ensures that your emails are less likely to be marked as spam.

To warm up a new domain, begin with a small number of emails and gradually increase the volume over several weeks. This is especially important if you want to send bulk emails.

2. Authenticate Your Emails

Email authentication is a key factor in building and maintaining a strong sender reputation. Setting up proper authentication protocols helps prove that your emails are legitimate and not from spammers or malicious actors.

Key Authentication Protocols

• SPF (Sender Policy Framework): This protocol verifies that the sending server is authorized to send emails on behalf of your domain.
• DKIM (DomainKeys Identified Mail): DKIM adds a digital signature to your emails to verify that they haven’t been altered during transit.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance): DMARC provides instructions for how to handle emails that fail SPF or DKIM checks and offers reporting on email authentication results.

Benefits of Authentication

• Increased Deliverability: Authenticated emails are less likely to be flagged as spam.
• Enhanced Security: Reduces the risk of email spoofing and phishing attacks.
• Improved Trust: Builds credibility with email providers and recipients.

3. Monitor Spam Complaint Rate

Spam complaints can significantly impact your sender reputation. When recipients mark your emails as spam, it signals to email providers that your messages are unwanted or irrelevant.

High spam complaint rates can lead to your emails being filtered or blocked by ISPs. Regularly monitoring your complaint rate helps you identify and address issues before they escalate.

4. Monitor IP/Domain For Blocklists

When an IP or domain gets blocklisted, it means that emails sent from your domain or IP are being flagged as spam by various servers, reducing the chances of reaching recipients' inboxes. This can happen if you send too many emails to invalid addresses, have a high spam complaint rate, or engage in poor email practices.

By keeping an eye on blocklists, you can quickly identify if your domain or IP has been flagged. Early detection allows you to take immediate action, such as submitting a request for removal from the blocklist and addressing the underlying issues that led to blocklisting—whether that’s improving your email list hygiene, reducing spammy content, or adjusting your sending frequency.

Regular monitoring also helps prevent future deliverability problems.

5. Remove Inactive Leads

Keeping your email list clean is vital for maintaining a strong sender reputation. Inactive leads, or those who haven’t engaged with your emails in a long time, can negatively impact your deliverability and reputation.

Inactive leads can contribute to high bounce rates and low engagement, which can harm your sender reputation and reduce email deliverability. Regularly removing or re-engaging inactive subscribers helps maintain a healthy, active list.

How To Manage Inactive Leads

• Regularly Clean Your List: Use tools to identify and remove inactive or unengaged email addresses.
• Re-engagement Campaigns: Send targeted campaigns to inactive subscribers to encourage them to re-engage. If they don’t respond, consider removing them from your list.
• Segment Your List: Focus your efforts on subscribers who are actively engaging with your content.

Conclusion

In summary, addressing email deliverability issues is crucial for ensuring your messages reach your intended audience and achieve optimal engagement. Here’s a recap of the key points:

• Understand the Causes: Email deliverability can be affected by factors such as spam filters, email authentication issues, high bounce rates, and low engagement. Recognizing these issues helps you target the right areas for improvement.
• Implement Effective Solutions: Regularly validate your email list, improve your sender reputation, monitor bounce rates and engagement, and optimize your email content to enhance deliverability.
• Use the Right Tools: Leveraging tools like Smartlead can significantly streamline this process. With features designed to monitor spam complaints, authenticate emails, and provide insights into deliverability, Smartlead helps ensure your emails land in the inbox where they belong.

By addressing these email deliverability issues and utilizing comprehensive tools, you can improve your email deliverability, leading to better engagement and more successful email campaigns.

Ready to improve your email deliverability? Try Smartlead today and ensure your emails reach the inbox!