What deliverability vendors or tools integrate with ESPs to analyze and improve email deliverability, and how are email deliverability issues diagnosed?
Michael Ko
Co-founder & CEO, Suped
Published 5 Jun 2025
Updated 19 Aug 2025
7 min read
Navigating the complexities of email deliverability can be challenging, especially when your emails aren't reaching their intended inboxes. It often leaves senders wondering if they need specialized tools that integrate with their existing Email Service Providers (ESPs) or a deep dive into diagnostic methods to pinpoint the issue. Understanding the interplay between your ESP's native capabilities and third-party deliverability solutions is key to ensuring your messages land where they belong.
Many businesses rely on their ESPs for sending bulk emails, but these platforms vary significantly in their built-in deliverability monitoring and improvement features. While some offer robust analytics, others might require external assistance to get a complete picture. This discussion explores the types of vendors and tools that integrate with ESPs, and outlines a systematic approach to diagnosing common deliverability problems.
Understanding integration types
Email deliverability tools and vendors often provide services that complement your ESP's capabilities, rather than replacing them. These third-party solutions typically offer more granular insights into inbox placement, sender reputation, and email authentication. They can help you understand why your emails might be hitting the spam folder or getting blocked altogether.
Many of these tools work by providing seed list testing, where your emails are sent to a diverse set of email addresses across various mailbox providers (like Gmail, Outlook, Yahoo) to see where they land. This gives you a snapshot of your inbox placement rate. Some tools also offer blocklist monitoring (or blacklist monitoring) to alert you if your sending IP or domain is listed, which can severely impact deliverability. Understanding what happens when your domain is blacklisted is crucial.
Integration capabilities vary. Some tools are designed to work seamlessly by connecting to your ESP's API, pulling data directly for analysis. Others might require you to export data or manually send test emails. For instance, some platforms offer direct integrations with major ESPs such as HubSpot, Salesforce Marketing Cloud, or Amazon SES. These integrations allow for automated monitoring and reporting, providing continuous insights into your email program's health. For more general information about improving email deliverability, explore comprehensive guides online.
Diagnosing deliverability issues
Diagnosing deliverability issues starts with observing symptoms and then systematically investigating potential causes. The first step is to check your ESP's internal reporting. Look at bounce rates, open rates, click-through rates, and complaint rates. A sudden spike in bounce rates, especially for soft bounces, might indicate a temporary issue with recipient servers or content filtering.
Beyond basic metrics, it is important to check your email authentication. SPF, DKIM, and DMARC are fundamental to proving your email's legitimacy to mailbox providers. Errors in these records can lead to emails being marked as spam or rejected entirely. Tools exist that allow you to send a test email and receive a detailed report on your authentication setup. This includes checks on your DMARC, SPF, and DKIM records, which are critical for deliverability. A helpful resource for quick technical checks is AboutMy.Email.
Another crucial diagnostic step is to monitor your sender reputation. Mailbox providers assign a reputation score to your sending IP addresses and domains based on various factors, including spam complaints, engagement rates, and blocklist presence. A low sender reputation is a common reason for emails landing in the junk folder. Some ESPs provide deliverability insights directly, but external tools often provide a more comprehensive view of your reputation across different providers.
Symptoms to watch for
Sudden drops: A sharp decline in open rates or an increase in unopens at specific mailbox providers, even when delivery rates appear normal.
Rejection messages: Reviewing bounce messages and SMTP codes from failed deliveries. These often contain clues about the reason for rejection.
Spam folder placement: If emails are consistently landing in spam or junk folders, it is a clear sign of a deliverability problem.
ESP capabilities versus specialized tools
While your ESP provides foundational sending capabilities, specialized deliverability tools often fill the gaps by offering advanced analytics and testing. ESPs typically provide general delivery metrics, but they may not offer deep insights into inbox placement across different ISPs. This is where a dedicated deliverability vendor can be invaluable.
These external tools often come with features like seed testing, blocklist checks, and even spam trap monitoring. Spam traps are email addresses used by ISPs to identify senders who are sending unsolicited mail. Hitting a spam trap can severely damage your sender reputation and lead to blacklisting (or blocklisting). Understanding how spam traps work is essential for proactive deliverability management.
The choice between relying solely on your ESP's features or integrating with a third-party tool depends on the scale and complexity of your email program. For high-volume senders or those experiencing persistent deliverability challenges, a specialized tool is often a worthwhile investment. It provides the deeper visibility required to diagnose complex issues and make informed decisions to improve your email deliverability. For a comprehensive guide on diagnosing email issues, review a dedicated email deliverability troubleshooting guide.
ESP native tools
Basic reporting: Provides core metrics like sent, delivered, bounced, opened, and clicked.
Delivery rate: Shows the percentage of emails accepted by recipient servers, but not necessarily inbox placement.
Limited insights: May not offer deep dives into why emails are going to spam or specific ISP performance.
Reputation monitoring: Tracks sender score, IP reputation, and domain reputation across various ISPs.
Actionable recommendations: Provides specific advice for improving deliverability based on diagnostic data.
Troubleshooting methodology
Effective deliverability troubleshooting involves a structured approach. Start by checking your email list hygiene. Sending to invalid or disengaged email addresses is a major red flag for mailbox providers. Regularly cleaning your lists, removing bounced emails, and re-engaging inactive subscribers can significantly improve your sender reputation. A high number of spam complaints can also negatively impact your deliverability, signaling to ISPs that your emails are unwanted.
Next, evaluate your email content. Content that triggers spam filters often includes excessive use of capitalization, exclamation marks, suspicious links, or certain keywords commonly associated with spam. It is also important to maintain a healthy text-to-image ratio and ensure your HTML is clean and well-structured. Personalization and relevant content can also boost engagement, which positively impacts deliverability.
Finally, monitor your engagement metrics closely. Low open rates and click-through rates, coupled with high complaint rates, indicate that your subscribers are not finding your emails valuable. This negative engagement can harm your sender reputation over time. Encouraging positive engagement, such as opens, clicks, and replies, signals to ISPs that your emails are desired and should be delivered to the inbox. Consistent monitoring of these metrics is vital for maintaining good deliverability, and understanding how to diagnose email deliverability issues is a continuous process.
Views from the trenches
Best practices
Always maintain a clean email list by regularly removing inactive or bounced addresses.
Implement robust email authentication protocols, including SPF, DKIM, and DMARC.
Monitor your sender reputation continuously using specialized third-party tools.
Segment your audience and personalize content to boost engagement and relevance.
Keep an eye on spam complaint rates and address feedback loop data promptly.
Common pitfalls
Ignoring bounce messages and soft bounces can mask underlying deliverability issues.
Sending to old, unverified, or purchased email lists that contain spam traps.
Using generic or spammy content that triggers filters and lowers sender reputation.
Over-relying on open rates as the sole measure of deliverability health.
Not having a clear strategy for re-engaging or removing inactive subscribers.
Expert tips
For comprehensive deliverability analysis, combine ESP data with insights from external tools.
Regularly test your email campaigns using seed lists to identify inbox placement issues.
Engage with mailbox providers' postmaster sites for direct insights and issue reporting.
A deliverability consultant can provide tailored advice for complex or persistent problems.
Focus on building positive sender reputation through consistent, valuable engagement.
Marketer view
Marketer from Email Geeks says that Postmastery offers monitoring tools that can integrate with most relevant ESPs, along with deliverability consultations.
2024-05-15 - Email Geeks
Marketer view
Marketer from Email Geeks mentioned that Inbox Monster is a great option for email deliverability.
2024-05-15 - Email Geeks
The path to better deliverability
Integrating deliverability tools with your ESP can provide a powerful combination for optimizing your email performance. While ESPs handle the fundamental sending infrastructure and offer basic reporting, specialized tools offer the advanced diagnostics and granular insights needed to truly understand and improve inbox placement.
By actively diagnosing issues through a combination of ESP metrics, authentication checks, reputation monitoring, and content analysis, you can proactively address challenges and ensure your email campaigns consistently reach their audience. Prioritizing both technical setup and content quality is essential for long-term deliverability success.
HubSpot, Salesforce Marketing Cloud, or Amazon SES. These integrations allow for automated monitoring and reporting, providing continuous insights into your email program's health. For more general information about improving email deliverability, explore comprehensive guides online.
