What are the best tools for tracking email deliverability outside of an ESP?
Michael Ko
Co-founder & CEO, Suped
Published 13 Jul 2025
Updated 19 Aug 2025
8 min read
Reliance solely on an email service provider (ESP) for deliverability insights can leave significant gaps in your understanding of how your emails truly perform. While ESPs offer valuable metrics on open rates, click-through rates, and bounces, their data often represents only a partial view of the deliverability landscape. This is because ESPs primarily report on what happens once an email is accepted by an inbox provider, not necessarily on the journey to that inbox, or why it might not have arrived in the first place.
To gain a comprehensive understanding of your email performance and ensure your messages consistently reach the inbox, you need to look beyond your ESP's dashboard. External tools provide critical insights into factors like sender reputation, blocklist (or blacklist) status, email authentication, and how your emails render across different clients.
These specialized tools offer a deeper dive into the technical aspects of email delivery, helping identify issues that ESPs might not detect or report. They are essential for proactive monitoring and troubleshooting, allowing you to optimize your sending practices and maintain a strong sender reputation.
Why ESP data isn't enough
While your ESP provides valuable metrics on campaign performance, the data is often limited to what they can observe from their servers. They might tell you about hard bounces, soft bounces, and spam complaints reported back to them, but they often lack visibility into why an email was blocked before it even reached a recipient's server or how it was filtered after acceptance. For example, an ESP might not clearly show if your IP or domain is on a specific blocklist, or if your authentication records are misconfigured in a way that causes widespread rejections by specific mailbox providers.
This limited view can create a false sense of security regarding your deliverability. You might see high reported delivery rates from your ESP, yet a significant portion of your emails could still be landing in spam folders or being outright rejected without your knowledge. This hidden problem impacts engagement, customer trust, and ultimately, your revenue.
Furthermore, ESPs typically aggregate data across all their clients, which can obscure issues specific to your sending patterns or domain reputation. To accurately diagnose and fix deliverability challenges, you need granular insights that external tools are specifically designed to provide. These tools can help you understand your actual inbox placement rates and diagnose specific problems.
ESP data limitations
ESPs provide metrics like open rates, click-through rates, and reported spam complaints, but often lack insight into pre-delivery filtering by mailbox providers. They report on emails accepted, not necessarily emails delivered to the primary inbox.
Their reporting can be aggregated, making it difficult to pinpoint specific issues affecting your domain or IP without deeper analysis. This can lead to a false sense of security.
Value of external tools
External tools offer granular data on pre-delivery blocks, email authentication failures, and blacklist status. They simulate sends to identify spam folder placement and rendering issues.
They provide proactive monitoring and detailed diagnostics, enabling you to identify and resolve deliverability problems before they significantly impact your campaigns.
Key types of external deliverability tools
To effectively track your email deliverability outside of an ESP, you need to leverage tools that specialize in different aspects of the email ecosystem. These fall into several key categories, each providing unique insights into your sending health. Combined, they offer a holistic view of your deliverability.
One of the primary concerns is your domain and IP reputation. Tools for reputation monitoring track your standing with internet service providers (ISPs) and major mailbox providers like Google and Yahoo. A strong reputation is crucial for avoiding spam folders and ensuring inbox placement. These tools often integrate domain reputation monitoring with other critical checks.
Another vital category is blocklist monitoring. Getting listed on a blocklist (or blacklist) can severely impact your deliverability, leading to widespread email rejections. Regular checks are essential to identify if your IP or domain has been listed and to take prompt action for delisting. These services often provide alerts if you appear on a major blocklist. Furthermore, email authentication tools are non-negotiable. SPF, DKIM, and DMARC are critical for proving your emails are legitimate and not spoofed, and external tools can validate their proper configuration.
Lastly, inbox placement testing tools are crucial. These services send your emails to a network of seed addresses across various mailbox providers and report where they land (inbox, spam, promotions, or blocked). This gives you a real-world perspective on how your emails are being filtered.
Ensuring proper email authentication
Email authentication protocols like SPF, DKIM, and DMARC are fundamental to email security and deliverability. They help mailbox providers verify that an email truly originated from the domain it claims to be from, which is vital for preventing spoofing and phishing attacks. Properly configured authentication records build trust with ISPs and significantly improve your chances of reaching the inbox, while misconfigurations can lead to rejections or spam folder placement.
Example SPF recordDNS
v=spf1 include:_spf.example.com ~all
DMARC reports provide valuable feedback on authentication failures, offering insights into potential spoofing attempts or issues with your legitimate sending sources. Regular monitoring of these reports is key to maintaining a healthy email ecosystem.
Leveraging free tools and dedicated platforms
Before investing in paid tools, it's worth exploring the robust free resources available. GooglePostmaster Tools is an invaluable, free service that provides insights into your sending reputation with Gmail. It offers data on spam rates, IP and domain reputation, feedback loop data, and DMARC failures. Similarly, Microsoft'sSmart Network Data Services (SNDS) provides similar data for their services, including Outlook.com and Hotmail. Using both of these is a fundamental step for any sender.
For more advanced monitoring, dedicated deliverability platforms offer a comprehensive suite of tools. These typically include seed list testing for inbox placement across various ISPs, blocklist monitoring with real-time alerts (for both private and public blocklists), and detailed DMARC reporting and analysis. Some even offer content analysis to identify potential spam triggers in your email creative.
While free resources are a great starting point, dedicated platforms often provide more frequent data updates, broader ISP coverage for inbox placement tests, and more sophisticated analytics. They can be particularly beneficial for senders with high email volumes or those experiencing persistent deliverability challenges.
Utilizing Google Postmaster Tools and Microsoft SNDS
Domain Verification: Verify your sending domains in both services to gain access to their respective dashboards. This is a crucial first step.
Reputation Monitoring: Regularly check your IP and domain reputation scores. A drop in score can indicate a deliverability issue.
Spam Rate Tracking: Monitor your spam complaint rates. High rates indicate poor list hygiene or irrelevant content, which can severely damage your reputation. Learn more in our guide to Google Postmaster Tools.
Feedback Loops: Utilize feedback loop data to quickly remove users who mark your emails as spam, preventing further complaints.
Actionable insights from external tools
Collecting data from various external tools is only the first step. The real value comes from interpreting this data and transforming it into actionable insights. Start by consolidating information from all your sources to identify patterns and potential root causes of deliverability issues.
For instance, if your inbox placement tests show emails landing in the spam folder at Yahoo but not Gmail, cross-reference this with your authentication reports and blocklist checks. Are you seeing DMARC failures specifically for Yahoo? Is your IP on a Yahoo-specific blacklist? These connections help you pinpoint the exact problem. You can then use this information to follow a proven checklist for improving deliverability.
Continuous monitoring is key to maintaining good deliverability. Deliverability is not a set-it-and-forget-it task, it requires ongoing attention. Regularly review your metrics from all external tools to spot trends and identify new issues as they arise. This proactive approach allows you to address problems quickly before they escalate and significantly impact your email program.
Analyze trends: Don't just look at single data points. Track your reputation, spam rates, and inbox placement over time to identify consistent patterns or sudden drops. This helps you understand if an issue is a one-off or a recurring problem.
Segment data: If possible, segment your deliverability data by recipient domain (e.g., Gmail, Outlook, Yahoo). This can reveal provider-specific filtering issues that require targeted solutions.
Address issues promptly: Whether it's a new blacklist entry (or blocklist entry), a sudden spike in spam complaints, or a drop in reputation, respond quickly. Delays can exacerbate the problem and make recovery more challenging.
Optimize content and list hygiene: Use insights from content analysis tools to refine your email copy. Continuously clean your email lists to remove inactive or problematic addresses that could be hurting your reputation.
Views from the trenches
Best practices
Actively use Google Postmaster Tools and Microsoft SNDS as your primary free data sources for reputation and spam rates.
Combine data from seed testing, blocklist checks, and authentication reports to get a holistic view.
Segment deliverability reports by major domain groups (e.g., Google, Microsoft, Yahoo) to identify specific issues.
Implement a consistent schedule for monitoring your email deliverability metrics.
Regularly clean your email lists by removing inactive subscribers and managing bounces efficiently.
Common pitfalls
Over-relying on ESP-provided deliverability metrics without validating them with external tools.
Ignoring DMARC aggregate reports, which contain critical data on authentication failures and sending sources.
Failing to monitor public and private blacklists (or blocklists) for your sending IPs and domains.
Not acting swiftly on deliverability warnings or drops in reputation scores.
Sending emails with content that triggers spam filters without knowing the specific issues.
Expert tips
Focus on sender reputation first, as it's the foundation for inbox placement.
A mix of free and paid tools often provides the most comprehensive insights.
Understanding the nuances of each mailbox provider's filtering rules is crucial.
Don't just track, actively use the data to refine your sending practices.
Prioritize email authentication (SPF, DKIM, DMARC) for improved trust and deliverability.
Marketer view
Marketer from Email Geeks says they really like 250ok for deliverability tracking and finds it helpful.
2019-05-20 - Email Geeks
Marketer view
Marketer from Email Geeks says they use Return Path for tracking deliverability.
2019-05-20 - Email Geeks
Achieving optimal deliverability
Effective email deliverability management goes beyond what your ESP can provide. By strategically incorporating external tools for reputation monitoring, blocklist checks, authentication validation, and inbox placement testing, you gain a clear, actionable picture of your email program's health. This multi-faceted approach allows you to proactively identify and resolve issues, ensuring your messages consistently reach your audience's inboxes and maximize the impact of your email communications.
Google and 
Yahoo. A strong reputation is crucial for avoiding spam folders and ensuring inbox placement. These tools often integrate domain reputation monitoring with other critical checks.
Microsoft'sSmart Network Data Services (SNDS) provides similar data for their services, including 
Outlook.com and 
Hotmail. Using both of these is a fundamental step for any sender.
Gmail, cross-reference this with your authentication reports and blocklist checks. Are you seeing DMARC failures specifically for Yahoo? Is your IP on a Yahoo-specific blacklist? These connections help you pinpoint the exact problem. You can then use this information to follow a proven checklist for improving deliverability.
