Summary
While email verification services play a role in list hygiene, their accuracy can be superseded by actual subscriber engagement. Experts widely concur that if a subscriber is actively interacting with your emails, their address should be considered valid, even if a verification service labels it as 'undeliverable' or 'risky.' This holds particularly true for 'catch-all' email addresses, which verification tools often cannot definitively confirm without direct interaction but are frequently legitimate and active. Marketers are strongly advised to prioritize their own first-party engagement data over technical flags from a verification tool when a contradiction arises, as proven subscriber activity offers the most reliable indicator of an email's health and value.
Key findings
- Engagement Trumps Verification: Direct subscriber engagement-opens, clicks, purchases-is consistently more reliable than the findings of email verification services, especially when those findings contradict active behavior. If a user is engaging, their address is effectively valid.
- Accuracy Limitations: Email verification services are not 100% accurate and can frequently produce false positives, flagging legitimate and active email addresses as undeliverable, risky, or unknown. No tool can achieve perfect precision.
- Catch-All Challenges: A significant limitation for verification tools lies with 'catch-all' email addresses. Services struggle to definitively confirm their validity without sending an actual email, leading to flags that might not reflect the address's true active status.
- Technical vs. Behavioral: Verification services primarily assess technical aspects like syntax and server responses, but they cannot gauge subscriber intent, engagement, or whether an email will actually be received and acted upon by a human. Active engagement provides this crucial behavioral insight.
Key considerations
- Prioritize Engagement Data: When a verification service flags an address but the subscriber consistently engages, always prioritize your own first-party engagement data. This direct interaction is the most reliable indicator of an email's validity and value.
- Strategic Service Use: Utilize email verification services primarily for reducing hard bounces and identifying definitively invalid addresses, but do not rely on them as the sole determinant of an email's deliverability or marketing worth. They are a tool, not a definitive verdict for engaged users.
- Handle Catch-Alls Carefully: Be mindful that 'catch-all' addresses are often legitimate, active accounts despite verification services' inability to confirm them definitively. If a 'catch-all' subscriber is engaged, continue sending to them, balancing the technical uncertainty with proven activity.
- Monitor Ongoing Performance: The true test of an email address's quality is its actual performance and recipient behavior. Continuously monitor your sending metrics and subscriber engagement over time, as this provides a more comprehensive and accurate picture than a one-time verification scan.
What email marketers say
9 marketer opinions
The accuracy of email verification services is a frequent topic, especially when their findings contradict tangible subscriber engagement. When a user actively interacts with your emails, this direct behavioral evidence consistently outweighs a verification service's technical assessment that might label the address as undeliverable or risky. Industry experts agree that such services, while useful for initial hygiene, are not perfectly accurate, often producing false positives or struggling with 'catch-all' addresses that are otherwise legitimate. In these scenarios, marketers are urged to place higher value on their own first-party engagement data, leveraging subscriber activity as the ultimate arbiter of an email's validity and deliverability.
Key opinions
- Engagement as Ultimate Validator: Active subscriber engagement-opens, clicks, conversions-serves as the definitive proof of an email address's deliverability and validity, overriding any conflicting flags from verification tools.
- Verification Tool Limitations: Email verification services, though helpful for hygiene, possess inherent accuracy limitations, frequently flagging legitimate and active addresses, particularly 'catch-all' types, as uncertain or risky without direct user interaction.
- False Positives are Common: It is widely acknowledged that verification tools can generate false positives, misidentifying truly active and valuable email addresses as problematic due to technical ambiguities rather than actual deliverability issues.
- Prioritizing Behavioral Data: The collective expert advice is to always prioritize a subscriber's demonstrable engagement history over a verification service's static assessment, especially for established, active contacts.
Key considerations
- Trust Your Engaged Audience: If a subscriber consistently engages with your content, maintain them on your active list regardless of a verification service's 'risky' or 'unknown' designation. Their engagement signals true validity.
- Strategic Application of Services: Employ email verification services primarily for new sign-ups, dormant segments, or to reduce hard bounces, but exercise caution and independent judgment when dealing with established, active subscribers.
- Recognize Catch-All Nuances: Understand that 'catch-all' addresses are often fully functional and active. Do not automatically suppress them based solely on a verification service's uncertainty, especially if engagement is present.
- Data-Driven Decision Making: Base your list management decisions on a holistic view of data, combining insights from verification tools with your own robust engagement metrics to ensure optimal deliverability and subscriber retention.
Marketer view
Marketer from Email Geeks explains that direct engagement data is always more reliable than list cleaning services and emphasizes that while validation tools can be used, verified opt-in is the most reliable method.
21 Jun 2022 - Email Geeks
Marketer view
Email marketer from Reddit explains that if a user is actively engaging with emails, their address is effectively valid regardless of a verification service's "undeliverable" or "risky" finding. They highlight that services might flag "catch-all" emails, which are often legitimate and active, as uncertain.
30 May 2023 - Reddit
What the experts say
3 expert opinions
When evaluating the quality of email addresses, experts highlight a crucial distinction: subscriber engagement often provides a more accurate assessment than standard email verification services. While these services are useful for technical checks like syntax or identifying known invalid addresses, they frequently fall short in predicting actual deliverability or, more importantly, a recipient's propensity to engage. Industry professionals advise that if a subscriber is actively interacting with your communications, such as making purchases or clicking links, their email address should be considered valuable, regardless of any flags raised by a verification tool. This emphasizes that real-world behavioral data offers the ultimate test of an email's health.
Key opinions
- Verification Limitations: Email verification services primarily assess technical validity, such as syntax and server responses, but cannot accurately predict subscriber engagement or actual message reception.
- Contradictory Results: Verification tools may produce inconsistent findings or fail to align with real-world subscriber activity, such as purchase data, leading to doubts about their definitive accuracy.
- Engagement as Definitive Proof: Actual subscriber behavior, including opens, clicks, and conversions, serves as the most reliable indicator of an email address's value and deliverability, effectively superseding technical verification statuses.
- Focus on Behavior: Experts emphasize that a subscriber's decision to engage makes their address valuable, even if a verification service might flag it based on technical or general risk assessments.
Key considerations
- Prioritize Engagement Over Tools: Marketers should trust their first-party engagement data more than a verification service's report when there's a contradiction, especially for active subscribers.
- Strategic Use of Verification: Employ email verification for initial hygiene, reducing hard bounces, and cleaning inactive segments, but understand its limitations for established, engaged users.
- Beyond Technical Checks: Recognize that an email address can be technically valid but still poor from a marketing standpoint due to lack of engagement, highlighting the need for a holistic view.
- Custom Solutions: For specific challenges like typo management, consider developing internal solutions tailored to your audience's unique engagement patterns rather than relying solely on external tools.
Expert view
Expert from Email Geeks shares an experience where multiple email verification platforms failed to agree or match actual purchase data, leading her to generally not recommend these services. She also mentions a client developing their own solution for typo management after discussing needs.
24 Jun 2023 - Email Geeks
Expert view
Expert from Spam Resource explains that email list validation services are limited to checking syntax and known bad addresses, but they cannot definitively determine if an address will receive mail or if the recipient will engage. He emphasizes that the ultimate test of an email address's quality, particularly when engagement data is available, is to send to it and observe actual subscriber behavior. If a subscriber is engaging, their address is valuable, even if a verification service might flag it based on technical checks alone.
11 Jul 2025 - Spam Resource
What the documentation says
3 technical articles
A key challenge for email verification services lies in their inability to definitively confirm the validity of 'catch-all' email addresses without actually sending a message to them. Documentation from leading providers such as Email Hippo, Hunter.io, and Verifalia explicitly states this technical limitation. This means that for 'catch-all' addresses, direct subscriber engagement becomes the most reliable, and often the only definitive, indicator of an address's functional validity. Consequently, marketers should prioritize their own engagement data, as proven interaction offers the most accurate assessment of deliverability and value, effectively overriding any technical uncertainty reported by a verification tool for these specific email types.
Key findings
- Catch-All Verification Limits: Email verification services inherently cannot definitively confirm the validity of 'catch-all' addresses without actually sending an email to them, a limitation widely acknowledged by providers like Email Hippo and Hunter.io.
- Engagement as Definitive Proof: For 'catch-all' addresses, direct subscriber engagement, such as email reception or interaction, becomes the most reliable and often the only definitive indicator of their functional validity.
- Services Classify as 'Deliverable': Despite the inability for full SMTP verification, services like Verifalia classify 'catch-all' addresses as 'Deliverable,' recognizing they can accept mail, which aligns with the idea that direct interaction confirms their active status.
- Override Uncertain Findings: Direct user interaction can effectively confirm or override an email verification service's uncertain finding for a 'catch-all' address, making your engagement data the ultimate arbiter.
Key considerations
- Prioritize Engagement for Catch-Alls: When dealing with 'catch-all' addresses, always prioritize direct subscriber engagement. If a user is active, consider the address valid, even if a verification service labels it as uncertain.
- Send to Confirm Catch-Alls: Recognize that sending an email is often the only definitive method to confirm the validity of a 'catch-all' address. Plan your email strategy to account for this nuance, allowing for engagement to prove deliverability.
- Balance Technical & Behavioral: For 'catch-all' addresses, blend technical verification insights with behavioral data. While the service might be uncertain, consistent opens and clicks indicate a functional and valuable address.
Technical article
Documentation from Email Hippo explains that it is inherently impossible for an email verification service to definitively determine the validity of a "catch-all" address without actually sending an email to it. This suggests that for such addresses, direct engagement data becomes the most reliable indicator of validity.
5 Sep 2022 - Email Hippo Documentation/Glossary
Technical article
Documentation from Hunter.io states that while their Email Verifier strives for high accuracy, no tool can be 100% precise, especially concerning "catch-all" email addresses. They explain that the only definitive way to confirm the validity of a catch-all address is to send an email to it, implying that direct interaction can confirm or override a service's uncertain finding.
18 Apr 2023 - Hunter.io Help Center
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