Summary
Experts, email marketers, and technical documentation overwhelmingly advise against directly verifying email addresses by connecting to servers. This practice can damage sender reputation, lead to blacklisting, and is often unreliable due to obscured server responses and anti-spam techniques. It can be seen as an abusive practice, akin to spamming. There are privacy concerns, as some verification services may harvest and resell email lists. Recommended alternatives include double opt-in, suppression lists, preference centers, segmentation, bounce management, multi-factor authentication, and using reputable third-party verification tools that do not rely on direct server connections.
Key findings
- Reputation Risk: Direct server verification significantly damages sender reputation, potentially leading to blacklisting by ISPs.
- Unreliable Results: Modern email systems often obscure the status of invalid addresses, making direct SMTP verification unreliable.
- Abusive Practice: Direct server connections for verification are viewed as aggressive and similar to spamming tactics.
- Privacy Concerns: Some verification services may harvest and resell email lists, posing a privacy risk to subscribers.
- False Positives: Address verification systems can produce false positives, removing valid email addresses from your list.
- Security Risks: The VRFY command in SMTP is often disabled due to security risks and the potential for abuse.
Key considerations
- Double Opt-In: Implement double opt-in to ensure subscribers have explicitly consented to receive emails.
- Suppression Lists: Utilize suppression lists to remove invalid or unengaged addresses from your mailing list.
- Preference Management: Provide clear and easy-to-use subscription preference options.
- Segmentation: Segment your email list based on subscriber behavior to send more targeted content.
- Bounce Management: Implement robust bounce management to automatically remove invalid addresses.
- Authentication: Implement SPF, DKIM, and DMARC to improve deliverability and sender authentication.
- 3rd Party Tools: Consider reputable third-party verification tools that use alternative methods for validation.
- Test Sends: Perform test sends to validate deliverability before blasting out large campaigns.
- Regular Hygiene: Establish a routine for cleaning and maintaining your email list.
- Privacy Due Diligence: Thoroughly vet any third-party email verification service to ensure ethical practices and protect subscriber data.
What email marketers say
10 marketer opinions
The consensus among email marketers is that directly verifying email addresses by connecting to servers is generally a bad idea. While it might seem efficient, it can damage your sender reputation, lead to blacklisting, and is often unreliable due to obscured server responses and techniques like greylisting. Many also carry privacy risks, some may harvest and resell your list.
Key opinions
- Reputation Damage: Direct server connection for verification can harm your sender reputation, potentially leading to blacklisting.
- Unreliable Results: Many servers intentionally obscure the status of invalid addresses to prevent harvesting, making SMTP verification less reliable.
- Spammer Tactics: Directly querying mail servers is often perceived as an aggressive tactic similar to those used by spammers.
- Privacy Issues: Some verification services may package and resell your email list, raising privacy concerns.
Key considerations
- Alternative Methods: Explore alternative verification methods like syntax checking, domain verification, double opt-in, and 3rd party validation services.
- Sender Authentication: Implement sender authentication protocols such as SPF, DKIM, and DMARC to improve deliverability.
- Bounce Management: Implement proper bounce management to remove invalid addresses from your list automatically.
- Test Sends: Carry out a test send to see how your list behaves before blasting out a campaign to everyone.
Marketer view
Email marketer from Hunter.io suggests that while email verification tools can be helpful, directly connecting to servers for validation can be problematic. They advocate using their own email verification system.
10 Sep 2021 - Hunter.io
Marketer view
Email marketer from ZeroBounce explains that using SMTP verification to validate emails directly has become less reliable. Many servers now intentionally obscure the status of invalid addresses to prevent harvesting. It is better to look at using more modern validation methods.
24 Mar 2022 - ZeroBounce
What the experts say
5 expert opinions
Experts strongly advise against directly verifying email addresses by connecting to servers. This practice is considered abusive, harms sender reputation, and is often ineffective due to blocking and obscured server responses. Furthermore, using unreliable verification services can lead to the deletion of valid email addresses and expose your list to harvesting and resale by malicious actors.
Key opinions
- Reputation Damage: Directly verifying email addresses via server connections can significantly damage your sender reputation.
- Ineffectiveness: Many modern email systems block or obscure responses to verification attempts, rendering them unreliable.
- Abusive Practice: This verification method is often viewed as abusive and akin to spamming tactics.
- Data Harvesting: Email verification services may harvest and resell your email list.
- False Positives: Address verification systems may produce false positives, removing good email addresses.
Key considerations
- Alternative Solutions: Explore alternative email verification strategies that don't involve direct server connections.
- Service Reliability: Carefully vet any email verification service to avoid those that use questionable tactics or pose privacy risks.
- Regular List Hygiene: Implement a robust email list hygiene program that includes methods beyond simple address verification, such as engagement-based cleaning.
- Privacy Awareness: Always be aware of the privacy implications of using third-party email verification services.
Expert view
Expert from Word to the Wise Staff explains that email list scrubbing tools carry privacy risks and should be fully checked. They may harvest and resell your list.
26 May 2024 - Word to the Wise
Expert view
Expert from Email Geeks warns that there’s at least one snowshoe spammer who is also selling a data hygiene service and that he sends his spam out to your list and then tells you what addresses bounced.
30 Aug 2024 - Email Geeks
What the documentation says
5 technical articles
Technical documentation and email service providers strongly advise against directly verifying email addresses by connecting to servers. The VRFY command in SMTP is often disabled due to security risks. Instead, methods such as double opt-in, suppression lists, preference centers, segmentation, bounce management, and multi-factor authentication are recommended to maintain a good sender reputation and ensure email validity. They recommend these practices because using outdated lists or improper validation methods can negatively impact your sender reputation.
Key findings
- Discouraged Practice: Direct server connections for email verification are generally discouraged due to security concerns and potential for abuse.
- Impact on Reputation: Using outdated or incorrect email lists, and practices like list bombing, can significantly harm your sender reputation.
- Alternative Methods: Double opt-in and suppression lists are recommended as safer and more effective methods for email validation.
- Preference Management: Managing subscription preferences and utilizing preference centers helps maintain list quality and sender reputation.
- Bounce Management: Implementing robust bounce management is essential for preventing bounce backs and maintaining a clean email list.
Key considerations
- Prioritize Opt-In: Focus on obtaining explicit consent from subscribers through double opt-in processes.
- Implement Suppression: Actively manage suppression lists to remove invalid or unengaged addresses from your mailing list.
- Manage Preferences: Provide clear and easy-to-use subscription preference options to allow subscribers to control the types of emails they receive.
- Segment and Personalize: Segment your email list based on subscriber behavior and preferences to send more targeted and relevant content.
- Regular List Hygiene: Establish a routine for cleaning and maintaining your email list to ensure data accuracy and improve deliverability.
- Multi-Factor Authentication: If applicable, implement multi-factor authentication to enhance the security and validity of email addresses.
Technical article
Documentation from Auth0 recommends multi-factor authentication as a more robust means of ensuring good email validity. They recommend sending a confirmation email to ensure the user does own the email address.
6 Jan 2022 - Auth0
Technical article
Documentation from Microsoft explains that practices like list bombing will impact your email reputation. They recommend implementing measures to prevent bounce backs and invalid emails.
9 Apr 2025 - Microsoft
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