Deliverability can sink your business in a matter of weeks. An email that doesn’t reach its recipient is a missed business opportunity.
According to recent studies, only 79% of marketing emails actually reach the inbox. The remaining 21%? They go to spam or are rejected by servers. For your prospecting campaigns, this is even more critical: every point of deliverability lost is as many potential deals evaporated.
What is a mail tester? How to use it practically? What are the best tools on the market?
In this guide, we explain everything you need to know to test and improve your email deliverability. Whether you’re launching your first campaign or managing thousands of sends, you’ll find the tools and methods here to keep your emails out of spam.
What is email deliverability?
Before diving into mail testers, let’s clarify what we mean by deliverability.
Deliverability is the percentage of your emails that actually reach your recipients’ inboxes (and not their spam folder or digital limbo).
The higher your deliverability rate, the more likely your campaigns are to reach their target. Otherwise, three catastrophic scenarios await you:
- You are identified as a spammer by Internet Service Providers (ISPs)
- Your campaigns are blocked upstream by mail servers
- Your statistics become unusable, making informed decisions impossible
To maximize your chances of reaching your contacts, your deliverability rate should exceed 95%. Below that, it becomes urgent to clean your lists to avoid multiplying hard bounces and soft bounces.
Why do we need a mail tester?
A mail tester is your diagnostic ally to understand why your emails aren’t reaching their destination, and more importantly, how to fix it.
The concrete benefits of a mail tester
Email testers allow you to:
- Estimate your potential deliverability before even hitting “send”
- Verify the technical validity of your setup (sending domain, servers, authentication)
- Check your sender reputation with major anti-spam filters
- Identify content issues that trigger filters (spam words, text/image ratio, suspicious links)
- Detect blacklists where you might be listed without knowing
In practice, a mail tester analyzes your email like Gmail, Outlook, or any other email service would. It simulates your message’s journey and tells you exactly what’s wrong.
When to use a mail tester?
Don’t test your emails once a year “just to see.” Deliverability needs continuous monitoring. Here are the key moments to run a test:
- Before each new major campaign: especially if you change format or target audience
- After a technical change: new domain, new server, new email signature
- As soon as your open rates drop: this is often the first sign of a deliverability problem
- Every 2-3 weeks for routine monitoring: to anticipate problems before they worsen
A mail test takes 2 minutes. A destroyed sender reputation takes months to rebuild. Do the math.
How to use a mail tester: a practical 5-step guide
Enough theory. Here’s how to practically use a free mail tester to check your deliverability in under 5 minutes.
We’ll use MailTester.com for this example, but the principle is similar for most tools.
Step 1: Access your free mail tester
Go to MailTester.com. No need to create an account, everything is instant.
The platform automatically generates a unique temporary email address that you will use as the test recipient. This address looks like: [email protected]
Step 2: Copy the provided test address
Copy the temporary email address displayed on the MailTester homepage. You only have a few minutes to send your test email before this address expires, so prepare your message in advance.
Step 3: Send your test email
Now, create an email exactly identical to the one you plan to send in your actual campaign:
- Same subject line
- Same content (text, images, links)
- Same signature
- Same sender address
- Same sending server
Send this email to the temporary address provided by MailTester. This is crucial: if you test an email different from the one you will actually send, the results will be worthless.
Step 4: Analyze your results
Return to MailTester and click “Then check your score.” In a few seconds, you’ll get a deliverability score out of 10.
MailTester analyzes:
- Your technical authentication (SPF, DKIM, DMARC)
- Your reputation with SpamAssassin
- Your content (spam words, text/image ratio, HTML quality)
- Your presence on blacklists
- The configuration of your mail servers
Each problematic element is detailed with its impact on your score.
Step 5: Identify actions to take
The mail tester provides a precise list of detected issues. Note down all red or orange points; these are your priorities.
The most common problems:
- Missing authentication (no SPF or DKIM configured)
- Spam trigger words in the subject or content
- Too many images compared to text
- Suspicious shortened links
- Absence of an unsubscribe link
Keep this report handy: we’ll see next how to act based on your score.
Key indicators tested by a mail tester
When a mail tester analyzes your email, it checks a series of technical indicators. Here’s what they really mean (without the jargon).
Technical Authentication: SPF, DKIM, DMARC
These three barbaric acronyms form the winning trio of email authentication.
SPF (Sender Policy Framework): It’s like a guest list for a party. SPF tells mail servers: “Here are the IP addresses authorized to send emails on my behalf.” Without SPF, anyone can claim to represent you.
DKIM (DomainKeys Identified Mail): It’s a digital signature that proves your email hasn’t been altered during transit. Imagine a wax seal on an official letter: if the seal is intact, the content is authentic.
DMARC (Domain-based Message Authentication): It’s the conductor that coordinates SPF and DKIM. It tells receiving servers: “If an email fails my SPF or DKIM tests, here’s what you should do with it” (reject it, mark it as spam, or notify me).
Without these three elements configured, your emails start with a severe handicap.
Server Configuration: MX Records
MX Records (Mail Exchange Records) tell the internet where to send emails destined for your domain. It’s the equivalent of a postal address for your emails.
If your MX Records are misconfigured, your prospects’ replies will never reach you. Worse: it can signal to ISPs that your infrastructure isn’t professional.
Reputation: Blacklists and SpamAssassin Score
Blacklists are blacklists of IP addresses or domains identified as spam sources. There are dozens of them (Spamhaus, Spamcop, Barracuda…).
Ending up on a blacklist guarantees that your emails will be blocked before even reaching the inbox. Mail testers check your presence on the main ones.
SpamAssassin is the most widely used open-source anti-spam filter in the world. It assigns points to your email based on various suspicious criteria. The higher your SpamAssassin score, the more likely you are to end up in spam. The goal: stay below 5 points.
Content: Spam Words, Text/Image Ratio, Links
Your content can betray you even with perfect authentication.
Spam words: certain words or phrases automatically trigger filters (“free,” “easy money,” “click here now,” “limited offer”). A single spam word won’t condemn you, but their accumulation will raise your spam score.
Text/image ratio: an email composed solely of a large image resembles a spammer technique to bypass text filters. Aim for at least 60% text.
Link quality: too many links, shortened links (bit.ly), links to dubious domains, or broken links all look bad.
How to improve your deliverability based on your score
You’ve tested your email. Now, let’s take action. Here’s what to do based on your deliverability score.
Score below 5/10: Urgent Actions
Your situation: Your emails have very little chance of reaching the inbox. You are likely already classified as spam by the majority of ISPs.
Priority actions:
- Configure your email authentication – SPF, DKIM, and DMARC are non-negotiable. Contact your host or IT department to set them up (it takes 30 minutes for a technician).
- Check blacklists – If you are listed, immediately start a removal process. Each blacklist has its own procedure (usually via a form on their website).
- Radically clean your contact list – Delete all invalid addresses, historical hard bounces, and contacts inactive for over 6 months. A tool like ZeroBounce or Bounceless can automate this cleaning.
- Completely review your content – Eliminate spam words, add more text if your email is too image-heavy, and ensure all your links work.
Do not restart any campaigns until your score reaches at least 7/10.
Score between 5/10 and 8/10: Recommended Optimizations
Your situation: You have the basics, but your deliverability is unstable. Some emails get through, others end up in spam depending on the filters’ mood.
Recommended actions:
- Optimize your content – Reduce spam words (replace “free” with “no cost,” “click here” with a more natural CTA). Improve your text/image ratio by adding written content.
- Add a visible unsubscribe link – This is a legal requirement, but it’s also a trust signal for anti-spam filters.
- Configure custom domain tracking – If you use an emailing tool, ensure your tracking links go through your own domain rather than a shared one. At La Growth Machine, this feature significantly improves deliverability.
- Segment your sends better – Avoid sending the same generic email to your entire list. The more targeted and relevant your message, the better your engagement rate (and thus your sender reputation).
- Space out your sends – Going from 0 to 5000 emails per day raises red flags for ISPs. Gradually increase volume over 2-3 weeks.
Score above 8/10: Maintenance and Monitoring
Your situation: Congratulations, your setup is solid. Now, you need to preserve this reputation.
Maintenance actions:
- Test regularly – A deliverability test every 2-3 weeks will allow you to detect problems before they impact your campaigns.
- Monitor your engagement metrics – Open rates and click-through rates are early indicators. If they suddenly drop, run another test immediately.
- Keep your list clean – Regularly remove inactive contacts and bounces. A list that no longer engages will gradually degrade your reputation.
- Use a warm-up process for new addresses – If you add a new sending address, don’t have it send 1000 emails on the first day. Start with small volumes and gradually increase.
Deliverability is not a permanent state; it’s a dynamic balance to maintain.
Mail Tester + LGM: the winning combo
Here’s how to combine the two approaches:
- Use a mail tester to diagnose your current deliverability status and identify technical issues
- Correct your setup (SPF, DKIM, DMARC, content)
- Launch your campaigns with LGM to maintain optimal deliverability through intelligent automation and multichannel prospecting
The advantage of multichannel prospecting? If your emails have a temporary deliverability issue, your LinkedIn messages, calls, or voicemails take over. You are no longer dependent on a single channel.
La Growth Machine also helps you target accurately: instead of sending 10,000 generic emails (hello bounces and spam), you send 1,000 highly targeted messages across multiple channels to qualified prospects. Less volume, more relevance, better deliverability.
Obtiens 3,5 fois plus de leads !
8 Tools to Test Your Email Deliverability (Free/Paid)
Now that we’ve laid the groundwork, let’s review the best mail testers on the market. To help you compare quickly, here’s a summary table:
Mail Tester Comparison Table
| Tool | Price | Verification Type | Ideal for |
|---|---|---|---|
| MailTester | Free | Spam score, authentication, blacklists, content | One-off tests, beginners |
| MailGenius | Free (paid consulting) | Spam score, subject line, links, authentication | SMEs seeking advice |
| Spamcheck | Free | HTML content, text/image ratio, links | Developers, technical analysis |
| Check (MailNJoy) | €4.8/1000 emails | Complete validation, catch-all, spam traps | List cleaning, French market |
| Bounceless | $19/month (2500 credits) | Syntax, DNS, servers, CRM integrations | MailChimp/HubSpot users |
| Bouncer | $7/month (2500 credits) | SMTP validation, simple interface, GDPR | List cleaning beginners |
| ZeroBounce | $16/month (2000 emails) | Validation, activity scoring, numerous integrations | Large databases |
| Debounce | $10/10K emails | SMTP check, catch-all, API, 115+ integrations | High volume, developers |
Check by MailNJoy – Subscription from €4.8 for 1000 verified emails
Let’s honor France by starting with a homegrown solution.
In addition to being RGPD compliant (General Data Protection Regulation) and hosting all data in France, the tool offers:
- Very advanced validation methods (Detection of spam traps, catch-alls, aliases, blacklisted emails…)
- The widest coverage of national and international ISPs
- Management of B2C or B2B emails
- Processing of your data imported via CSV or a dedicated API
- Export of PDF reporting
- Good customer service
- A very affordable price
To access the lowest verification level, expect less than €5 for 1000 emails, €24 for 10K emails, up to €1600 for 2.5M verifications.
MailTester – completely free
This is probably the best-known of all the solutions we’ll mention in this article.
Its operation is super intuitive and allows you to check the quality of your email address at a glance.
By visiting the MailTester website, you are invited to send an email to a generic address. You can then check the spamminess of your emails.
Mail Tester checks:
- Your email content
- Your reputation score with SpamAssassin
- Your authentication level (DKIM signature, DMARC test, server association…)
- Potential blacklists you are registered on.
Good to know:
SpamAssassin is an open-source software recognized in the field of unwanted email filtering. It runs a battery of tests on sent emails. Based on the results, it assigns a score to your message. The higher this score, the more likely your email is to be classified as SPAM.
Bounceless – 100 credits offered, subscription from $19/month
Bounceless is a user-friendly email cleaner from California.
It stands out from the competition with a polished UX and practical features:
- Importing CSV or using an API to upload your email list
- The ability to upload up to 500,000 contacts at once
- Verification of your email syntax
- Check of DNS and your mail servers
Another major strength of Bounceless is its ability to connect with numerous CRM tools, such as MailChimp, HubSpot, SendGrid, Sendloop…
The more volume you want to process, the more you’ll have to pay. Expect $19 for 2500 email verifications, $99 for 25K emails, or $700 for 500K verifications.
The good deal:
For any free registration, Bounceless offers you 100 email verification credits.
Bouncer – 100 free credits, then subscription from $7/month
Bouncer is the perfect simplification for deliverability novices.
Its interface is polished and perfectly accessible to everyone. There are many advantages we appreciate:
- The highlighted statistics are understandable by the average marketer
- Data processing is GDPR-Friendly
- The API is easy to implement
- Numerous integrations with mailing tools
- The quality of customer service
All these advantages are reflected in its price, which is slightly higher than its counterpart Bounceless.
Expect $17 for 2500 emails, $125 for 25K emails, and $1000 for 500K emails.
The good deal:
Here too, Bouncer offers you 100 free email verifications before you need to subscribe to a paid plan.
MailGenius free (without consulting)
With over 625,000 clients, MailGenius is a heavyweight among Email Service Providers (ESPs).
Based on the same principle (for the free plan) as MailTester, it allows you to check the spamminess of your email address in seconds. Additionally, you can:
- Schedule a free 30-minute call to discuss your deliverability with an expert
- Estimate the effectiveness of your email subject line
- Ensure you comply with authentication standards
- Avoid anti-spam filters
- Check for broken links in your content
- Consult your listing on blacklists
ZeroBounce 100 emails free, subscription from $16/month
Another tool with “bounce” in its name and a freemium version. By subscribing, you can:
- Verify recipient email addresses
- Score the activity of each email address
- Process a large amount of data thanks to Zerobounce’s easy-to-implement API
- Eliminate hard bounces
- Bypass spam traps
- Integrate the tool with numerous platforms like Shopify, Mailchimp, Slack, Zoho, HubSpot…
The starting plan is set at $16 for 2000 emails, with a decreasing price per email verification based on the volume processed (up to 1M emails for $2250).
The good deal:
Once again, ZeroBounce offers you 100 free email address verifications before you need to subscribe to a paid plan.
Spamcheck completely free
It’s hard to find a tool simpler to use than Spamcheck.
It’s an excellent spam radar, based on your email content. To use it, you need to copy-paste the HTML code of your email, including headers. Then, the tool examines:
- Link quality
- Your HTML content quality
- Compliance with your domain’s authentication standards
- The text/image ratio
The goal? To get the lowest possible SpamAssassin score.
Debounce 100 free credits, subscription from $10
This is one of the most comprehensive email validation tools. It includes numerous features such as:
- SMTP check
- The ability to verify addresses directly on the platform via an API
- Verification of email address syntax
- Domain name confirmation
- Catch-all and spam trap checks
- Duplicate removal
- Shared account for the whole team
- Export of collected data
At the time of writing this article, the platform offers over 115 integrations (Zapier, Zendesk, HubSpot, Mailchimp, Mailgun, Mailjet, SendInBlue, Lemlist, MailerLite, Shopify, Stripe, Typeform, Zoho…).
Another significant point, Debounce is one of the cheapest tools in our selection. Expect $15 for 10K email verifications, $90 for 100K emails. For larger accounts, it’s possible to verify up to 5M email addresses for $1500.
Key Takeaways
Checking your deliverability quality is not a luxury, it’s an absolute necessity for sustainable business growth.
Essential points to remember:
✅ Test before sending: A free mail tester like MailTester gives you a complete diagnosis in 2 minutes. Use it systematically before your important campaigns.
✅ Aim for a score of 8/10 minimum: Below that, your deliverability is compromised and your emails risk ending up in spam.
✅ Authentication is not optional: SPF, DKIM, and DMARC must be configured. It’s the foundation of your technical credibility.
✅ Clean your lists regularly: An erroneous email is a lost prospect. Hard bounces destroy your sender reputation. Use a validator like ZeroBounce or Debounce to maintain a healthy list.
✅ Continuous monitoring: Deliverability is not a fixed state. Test every 2-3 weeks and after any technical change.
✅ Prevent rather than cure: Mail testers diagnose, but tools like La Growth Machine help you build optimal deliverability from the start through custom domain tracking, sending from your professional addresses, and multichannel prospecting.
Obtiens 3,5 fois plus de leads !