How accurate are email verification services when subscriber engagement contradicts their findings?
Matthew Whittaker
Co-founder & CTO, Suped
Published 14 Jun 2025
Updated 18 Aug 2025
7 min read
It is a common scenario in email marketing: you run your subscriber list through an email verification service, and it flags a segment of your audience as risky or invalid. Yet, when you look at your internal engagement data, these same subscribers are actively opening your emails, clicking on links, and in some cases, even making purchases. This contradiction can be puzzling.
Email verification services play a crucial role in maintaining list hygiene by identifying and removing invalid, non-existent, or risky email addresses. This process helps reduce bounce rates, protect your sender reputation, and ultimately improve your overall email deliverability. The aim is to ensure your messages reach legitimate inboxes and avoid issues like being added to an email blocklist (or blacklist).
However, the inherent challenge lies in their methodology. These services use various techniques, including real-time SMTP checks, syntax validation, domain checks, and spam trap identification, to assess an email's validity. While generally effective, their findings are based on a snapshot in time and may not always capture the full dynamic picture of an active subscriber.
When your direct engagement metrics tell a different story, it is essential to understand why these discrepancies occur and how to prioritize the data for optimal email marketing performance. Balancing external verification results with your internal subscriber behavior is key to effective list management and robust deliverability.
The challenge of conflicting data
The conflict between an email verification service's findings and your own engagement data is a common point of confusion for many email marketers. We rely on these services to clean our lists and prevent issues like high bounce rates or landing on an email blacklist, but what happens when their assessment directly contradicts tangible proof of subscriber interest?
Your internal engagement data, encompassing opens, clicks, and conversion events, provides the most direct and undeniable evidence of a subscriber's activity and value. If a subscriber is consistently opening your emails, clicking links, or even completing purchases, they are clearly engaged. Discarding such a valuable lead based solely on an external tool's risky classification can be detrimental to your marketing efforts and revenue.
This challenge highlights the need for a nuanced approach to list hygiene. While verification services offer a critical first line of defense against harmful addresses, they should not be the sole determinant of whether a subscriber remains on your list. Understanding the impact of email verification on engagement means recognizing when your first-party data should take precedence.
Verification service assessment
Status: Email flagged as risky,invalid, or catch-all due to various checks.
Basis: Likely based on SMTP server responses, domain reputation, or perceived risk of spam traps.
Real subscriber behavior
Engagement: Consistent opens, clicks, form submissions, or even previous purchase history.
Basis: Direct interaction with your email campaigns and business.
Why verification services aren't always 100% accurate
Email verification services, while valuable, are not infallible. Their accuracy depends on various factors, and false positives can occur. One primary reason for discrepancies is the dynamic nature of email servers. A temporary network issue or an ISP performing maintenance can lead to a risky or unknown status that isn't indicative of a permanently invalid address.
Another factor is the presence of catch-all domains. These domains accept all incoming email, regardless of whether the specific address exists, making it impossible for verification services to definitively confirm validity without actually sending an email. Such addresses are often flagged as risky even if they belong to active subscribers. The level of accuracy can vary between services.
Common reasons for discrepancies
Temporary server issues: An email server may be temporarily down or undergoing maintenance during the verification process.
Catch-all domains: Domains that accept all emails sent to them, making precise validation difficult for services.
Aggressive algorithms: Some services may err on the side of caution, flagging borderline addresses as risky.
Aging data: Verification results can become outdated quickly as email addresses become inactive or are repurposed.
It is important to remember that these services provide a valuable external perspective, especially for newly acquired lists or those with unknown provenance. However, when faced with active engagement, their findings should be weighed against the empirical data you have collected directly from your subscribers. Your own system's interaction history is a powerful signal that often outweighs the generic classifications of a third-party tool.
Prioritizing internal engagement data
When internal engagement data conflicts with email verification findings, your own data should generally take precedence. Internet Service Providers (ISPs), like Google and Yahoo, track a wide array of engagement signals directly from their users. These signals are the true indicators of a subscriber's interest and impact your sender reputation and deliverability far more than a third-party's assessment.
Engagement signals include email opens, clicks on links within the email, replies, marking emails as not spam, adding your address to their contacts, and even deleting emails without opening them. ISPs analyze these behaviors to determine how relevant your emails are to their users. Consistently positive engagement signals a healthy sender, while poor engagement or high bounce rates can lead to your emails being filtered to the spam folder or even your IP being added to a blocklist.
Understanding how internet service providers track email engagement is critical. Your internal data directly reflects this. If a subscriber on your list is showing active engagement (opens, clicks, purchases), removing them because a verification service flagged them as risky could hurt your marketing performance. It can also hurt your sender's reputation by removing engaged users and focusing on less reliable data.
Data source
Accuracy
Actionability
Email verification service
High for basic validation (syntax, domain existence), but prone to false positives for catch-all or temporary issues.
Good for initial list cleaning and removing hard bounces before sending. Less reliable for active users.
Internal engagement data
Reflects actual user behavior, making it the most accurate measure of subscriber value and deliverability performance.
Essential for segmenting, re-engagement campaigns, and identifying highly valuable subscribers. Drives long-term deliverability.
Strategies for managing your email list
Navigating the complexities of email verification and subscriber engagement requires a balanced strategy. The goal is to maximize deliverability while retaining valuable, engaged subscribers. Rather than blindly trusting a verification service's risky flags, integrate these insights with your own robust engagement metrics.
For new subscribers, implementing a double opt-in process is paramount. This ensures that the email address is not only valid but also that the subscriber genuinely wants to receive your emails. For existing lists, especially those with older single opt-in data, use verification services as a guide, but always cross-reference with your engagement history. If a user is actively engaging, keep them. If they are flagged as risky but show no engagement, consider a re-engagement campaign before removal.
Continuously monitor your deliverability and sender reputation metrics through tools like Google Postmaster Tools. Pay close attention to bounce rates and spam complaint rates, as these are direct signals to ISPs about your list quality. Proactive list hygiene, combining various email verification strategies with a strong focus on engagement, will yield the best results for your email program.
Example of a simple email list segmentation ruleSQL
IF (email_open_count > 0 AND last_open_date >= "2023-01-01") OR (email_click_count > 0 AND last_click_date >= "2023-01-01") THEN KEEP_SUBSCRIBER
Views from the trenches
Best practices
Always prioritize your direct engagement data (opens, clicks, purchases) over third-party verification service findings, especially for active subscribers.
Implement double opt-in for all new subscribers to ensure high-quality and verified consent from the start.
Segment your audience based on engagement levels, targeting highly engaged subscribers with your main campaigns and creating re-engagement paths for less active ones.
Monitor your bounce and spam complaint rates closely as key indicators of list health and deliverability issues.
Common pitfalls
Blindly removing subscribers marked as 'risky' by a verification service without cross-referencing their engagement history can lead to losing valuable customers.
Relying solely on external verification without considering temporary server issues or catch-all domains can lead to inaccurate list cleaning decisions.
Neglecting ongoing list hygiene and only performing verification sporadically, as lists decay rapidly over time.
Ignoring the signs of low engagement or high complaints, which are stronger indicators of poor list quality than a one-time verification scan.
Expert tips
Utilize email verification services primarily for cleaning stale, purchased, or newly acquired lists with no prior engagement data.
Develop an internal scoring system that factors in opens, clicks, and conversions to identify truly valuable subscribers, irrespective of external verification statuses.
Consider a phased approach: quarantine 'risky' but engaged subscribers and monitor their next few sends closely before making a final decision.
Regularly audit your email sending practices to ensure compliance with best practices, further reducing the reliance on external verification for active lists.
Marketer view
Marketer from Email Geeks says that direct engagement data will consistently be more reliable than insights from list cleaning services.
August 10, 2024 - Email Geeks
Expert view
Expert from Email Geeks says that their client tested multiple verification platforms, and none provided consistent results or aligned with actual purchase data. They generally do not recommend data hygiene services as a primary solution.
August 10, 2024 - Email Geeks
Balancing external insights with internal reality
When email verification services flag engaged subscribers, it presents a clear conflict between external assessments and your internal reality. While these services are valuable for maintaining a clean list and preventing issues like high bounce rates or landing on an email blocklist, their findings should be interpreted with caution, especially when contradicted by concrete engagement data.
Ultimately, your own historical engagement data – opens, clicks, and conversions – remains the most reliable indicator of a subscriber's value and deliverability. By prioritizing these internal metrics, implementing robust opt-in processes, and continuously monitoring your sender reputation, you can ensure your email marketing efforts are both efficient and effective, reaching those who truly wish to hear from you.
Google and 
Yahoo, track a wide array of engagement signals directly from their users. These signals are the true indicators of a subscriber's interest and impact your sender reputation and deliverability far more than a third-party's assessment.
