top of page

Optimize and Improve Your Campaigns: How to Test Email Deliverability?

Updated: Jun 21

Every day, billions of emails travel through the digital universe.

Whether you're sending an email campaign to thousands or a single message to a colleague, the last thing you want is for that email to land in the spam folder.

Email deliverability is a critical factor that often goes overlooked.

In this comprehensive guide, we'll take a look at:

how to test email deliverability

What Is Email Deliverability?

Email deliverability is the measure of how successfully your emails land in the recipient's inbox without being filtered out by spam filters.

It's not just about whether your email gets sent, it's about where it ends up.

You could use the most sophisticated email service providers, but if your emails are getting stuck in the spam folder or not reaching the inbox at all, you have a deliverability issue.

Various factors, including domain reputation and IP addresses, influence your email's journey from the sender to the recipient.

Understanding and optimizing these can dramatically improve your email deliverability.

What Affects Email Deliverability?

Before testing email deliverability, you first need to understand what factors influence it.

Then, you’ll be better equipped to deal with any less-than-amazing numbers.

1. Domain Reputation

Your domain reputation plays a large part in whether your emails make it to the inbox or get caught in spam filters.

A domain with a good reputation is more likely to pass through popular spam filters, positively affecting your email deliverability.

Domain reputation is built over time and is affected by various factors, such as the volume of emails sent, how many of them are marked as spam, and the quality of email content.

Email scraping tools can help you gather email addresses, but it's crucial to verify these addresses to maintain a good domain reputation.

2. IP reputation

Similar to domain reputation, IP reputation also has a significant impact on your email deliverability.

Each outgoing email is sent from an IP address, and this address carries its reputation, known as the sender score.

The sender's reputation is evaluated by email servers before deciding where your email will land.

If you're sharing an outbound IP address with others who have poor email practices, it can negatively affect your own deliverability.

3. Engagement metrics

Engagement metrics such as open rates, click-through rates, and bounce rates also influence email deliverability.

Email providers look at how users interact with your emails.

If your emails are often opened, moved out of the spam folder, or replied to, these positive actions signal to spam filters that your emails are wanted, improving your sender's reputation and overall email deliverability.

These are some of the most common engagement metrics that can affect deliverability:

  • Open rate: This key indicator reveals the portion of recipients who actually open your email.

  • Click-through rate (CTR): This metric tells you the fraction of recipients who were intrigued enough to click on at least one link in your email.

  • Click-to-open ratio: By dividing unique clicks by unique opens, this ratio sheds light on the quality of your email content. It's a measure of how many people were interested enough to explore further after opening your message.

  • Time spent on email or page: This captures the amount of time a recipient invests in digesting your email or browsing a linked landing page. It's akin to someone thoroughly reading a newspaper article, rather than just skimming the headlines.

  • Conversion rate: This rate reveals the slice of recipients who not only clicked a link but took a meaningful action like making a purchase or filling out a form.

  • Bounce rate after visiting: In the website context, this shows the portion of visitors who leave after seeing just one page. Imagine someone walking into a store, glancing around, and walking right out again; that's what this metric helps you understand.

  • Spam flags: This counts how often your emails get marked as spam. It's a red card in your game of email marketing, signaling that you need to improve your tactics.

  • Unsubscribe rate: This rate captures the frequency at which recipients opt to no longer receive your emails.

  • Forwards: This metric keeps tabs on the number of times your email gets shared or forwarded. Think of it as your audience doing your marketing for you, signaling a job well done!

​Want to get a deeper look into email metrics? Read about 8+ email marketing metrics you need to track and start monitoring your campaigns like a pro!

When & How to Test Email Deliverability

So, now you have a handle on what email deliverability is and what factors can affect it. But when should you actually test it?

Certain triggers, like a dip in open rates or an increase in spam flags, should prompt you to investigate your email deliverability.

Below are methods to help you optimize your email campaigns.

a) Authentication Testing

One of the first steps in having your emails reach the inbox is to verify the authentication records for your domain and IP address.

Without proper authentication, your emails are much more likely to be flagged by spam filters.

Using various online tools, you can instantly check if your SPF records and other authentication protocols are set up correctly.

Periodic reviews and updates to your authentication records are recommended.

b) Email Content Testing

The content of your email can dramatically affect where your email lands, be it the inbox, the spam folder, or somewhere else entirely.

If your content triggers a 550 high probability of spam message, it indicates that your email is likely being flagged by spam filters, requiring immediate content revisions.

Elements like subject lines, message body, links, and even the tone of the message are scanned by spam filters.

It's crucial to test email content before sending it to your entire list.

For this, you can use email deliverability testing tools to get a comprehensive deliverability report.

This will highlight any red flags and offer suggestions for improvement.

Consider also the image-to-text ratio in your emails and avoid certain trigger words that could flag your email as spam.

Additionally, learning how to send an email to multiple recipients individually can help maintain personalization and reduce the chances of your emails being marked as spam.

This practice ensures that each recipient feels valued and reduces the likelihood of triggering spam filters.

c) Subject Line Testing

Never underestimate the power of a compelling subject line.

Not only does it affect open rates, but it's also one of the first things spam filters scrutinize.

Use testing tools to check how your subject line performs and adjust as needed to improve inbox placement.

A/B testing can help you identify which subject lines are the most effective. However, be cautious of using "clickbait" subject lines that don’t accurately reflect the content, as this could hurt your sender's reputation.

d) Email List Testing

The quality of your email list can also affect deliverability.

Sending emails to inactive or non-existent addresses can hurt your sender's reputation.

Before you send out any email campaign, it's advisable to use list verification tools.

These tools will identify any problematic addresses and help you maintain a healthy email list.

During this process, you should specifically look out for 550 permanent failure errors, which occur when emails are sent to addresses that no longer exist or were never valid.

By cleaning these from your lists regularly, you can prevent these bounce back messages that negatively impact your domain's sender score.

Consider list segmentation to send more targeted emails, which can also improve your deliverability.

Don’t forget to manage and remove bounced emails from your list to maintain a strong sender reputation!

A great tool for testing your email list and deliverability is EmailListVerify. With EmailListVerify you can:

  • Perform syntax error and SMTP validation

  • Eliminate redundant email addresses effortlessly

  • Utilize EmailListVerify's hard bounce checker to discreetly confirm whether an email address is active and can receive messages.

  • Use the MTA validator to make sure there's a responsible email server available to accept messages.

  • Incorporate EmailListVerify's real-time API to proactively verify email addresses before they even enter your database.

  • Boost your sender reputation by identifying and clearing out spam traps using EmailListVerify.

  • Have a go-to bulk email verifier, capable of verifying multiple email addresses in one go.

Top 6 Email Deliverability Testing Tools

Email deliverability testing is an essential component of any successful email campaign.

Utilizing the right tools can provide invaluable insights into how your emails perform and where they land.

These are some of the top email deliverability testing tools that can help you achieve better results.

1. Warmup Inbox

Warmup Inbox tester is a highly recommended tool for those looking to check their email deliverability.

Not only does it check your emails against popular spam filters completely for free with its spam checker tool, but as a email warmup service, it also offers several other capabilities to boost all of your email marketing efforts:

  • Boosts email deliverability to reach prospect inboxes

  • Helps you to avoid spam folders and blacklists

  • Tracks and improves sender reputation with Warmup Inbox

  • Lands emails in primary Inboxes for better open rates

  • Notifies you if your reputation score drops

  • Fills up your inbox with quality emails and avoid spam

  • Monitors domains to stay off blacklists

  • Uses real-time tracking for campaign progress

This service helps you gradually increase your email volume, which can greatly improve your domain and IP reputation over time.

Its free version is quite robust, and paid plans offer even more comprehensive email warmup features.

2. Mail-tester

Mail-tester offers a free tool that allows you to send a test email to a specified address, after which you'll receive a detailed analysis of your email.

This includes your spam score, which is a numerical representation of how likely your email is to end up in the spam folder.

With its straightforward interface, it's an excellent tool for users who need quick insights into their email deliverability.

3. Glock Apps

Glock Apps offers a comprehensive deliverability report, allowing you to understand why your emails might not be reaching the inbox.

It tests your email on various email clients and providers to give you a broad view of its performance.

You can also test email content and sender reputation, making it a well-rounded tool for all your email deliverability needs.

4. Mailreach

Mailreach is another reliable option for checking your email's likelihood of landing in the spam folder.

It offers various metrics, including sender score and domain reputation, to provide a complete picture of your email's performance.

This tool can also integrate with your existing email service providers for seamless testing.

5. GMass

GMass offers tools that go beyond just spam check and deliverability testing.

It also helps you with your email campaigns, offering a suite of features that can improve both your delivery rates and engagement.

GMass is especially good for businesses that send out high volumes of emails.

6. MxToolbox

MxToolbox is a versatile tool that offers a range of services from simple spam checks to detailed deliverability reports.

Its delivery rates test and other features provide a thorough analysis of how your emails perform, offering insights you can act on to improve your email strategy.

In the fast-paced digital world, ensuring your emails reach the inbox is more critical than ever.

From crafting engaging content to selecting the right tools, mastering email deliverability can seem like a complex process, but it need not be.

With proper testing and monitoring, you can significantly improve the likelihood of your emails landing in your audience's inbox rather than their spam folder.


Taking advantage of specialized tools for testing deliverability and optimizing each component – be it your domain reputation or the subject line – can yield exceptional results.

Don't underestimate the power of email as a communication channel; make sure you give it the attention it deserves!

Now you're armed with all the information you need to tackle email deliverability head-on.

Start testing, keep monitoring, and you'll find that your efforts pay off in higher engagement, better customer relationships, and ultimately, increased ROI.

Good luck!


Start landing in more inboxes. 
Use Warmup Inbox to improve your sender reputation and increase your deliverability.

No credit card needed!

bottom of page