Is it possible to validate email addresses based on open activity from other senders?
Michael Ko
Co-founder & CEO, Suped
Published 15 Apr 2025
Updated 16 Aug 2025
8 min read
Many email marketers dream of knowing whether a recipient is actively opening messages, not just from their campaigns, but from *any* sender. Imagine the power of pruning your list to only those truly engaged, leading to highly targeted reactivation efforts and significantly improved deliverability. It's a compelling idea, especially when trying to re-engage past active subscribers without risking your sender reputation.
However, the reality of validating email addresses based on open activity from other senders runs into significant barriers. While the desire to identify the most responsive subscribers is understandable, the mechanisms for doing so across different sending entities are generally non-existent. This isn't just a technical hurdle, but a fundamental issue rooted in privacy and data security principles that govern email communication today.
The privacy barrier
The primary reason why validating email addresses based on open activity from other senders is not possible stems from the inherent privacy architecture of email. When you send an email, any open tracking is typically facilitated by a tiny, invisible image (a tracking pixel) unique to your campaign and your sending platform. When a recipient opens your email, this pixel loads, registering an open on *your* analytics platform. This data is first-party data, belonging to you and your relationship with that subscriber.
Mailbox providers, like Google or Microsoft, do not share their users' aggregate or individual open activity with third parties, including other email senders. This would be a massive breach of user privacy and a violation of data protection regulations such as GDPR and CCPA. Their primary responsibility is to protect their users' data, not to facilitate cross-sender engagement tracking. Even Google states that it cannot verify the accuracy of open rates reported by third parties. You can read more about this in their email sender guidelines.
Any service claiming to offer such a capability would either be engaging in highly intrusive and likely illegal data collection, or simply providing aggregated, non-specific data that isn't truly tied to individual open activity across different senders. The privacy safeguards in place are precisely designed to prevent this type of cross-pollination of user engagement data without explicit consent.
Technical limitations and current validation methods
Traditional email validation methods focus on verifying the structural integrity and existence of an email address. This typically involves several checks:
Syntax check: Ensures the email address conforms to standard formatting rules.
Domain validation: Checks if the domain exists and has valid MX (Mail Exchange) records.
SMTP server check: Attempts to connect to the email server to confirm the address is deliverable. This is often done without sending an actual email, for example by using the VRFY or EXPN command, though many servers block these for security reasons. You can learn more about this in our guide: Should I validate email addresses using SMTP commands?
These validation steps determine if an email address is valid and deliverable, but they provide no insight into whether the user actively opens emails from other senders. An email verification service can confirm an address exists and accepts mail, but it cannot tell you the user's engagement habits across other companies' emails. For a broader understanding of validation, consider checking how to check if an email is valid.
Standard email validation
Focuses on technical deliverability. Determines if an email address is properly formatted, the domain is valid, and if the mailbox exists. Does not provide data on user engagement or activity beyond basic deliverability. This is critical for avoiding bounces and managing blocklist (or blacklist) risks.
Identifying harmful addresses
Tools can identify spam traps, disposable email addresses, and other problematic contacts that could damage your sender reputation. This is a crucial aspect of maintaining a clean email list.
Alternative approaches for re-engagement
Since you can't validate email addresses based on open activity from other senders, the most effective strategy for re-engagement and maintaining a healthy list involves focusing on your own first-party data and smart list management practices. Your engagement metrics, such as opens, clicks, and conversion rates from *your* previous campaigns, are the most reliable indicators of subscriber interest. ISPs track positive engagement as a key deliverability signal.
For reactivation efforts, segmenting your list based on recency and frequency of engagement with your brand is crucial. For instance, you might identify subscribers who haven't opened or clicked an email in 6-12 months but have previously shown engagement. Rather than trying to find a service that offers cross-sender open data, focus on a strategic re-engagement campaign designed to prompt a response.
This could involve a series of emails with compelling offers, surveys to understand their current interests, or updates on new products or services. The goal is to re-establish a direct relationship with these subscribers. If they don't respond after several attempts, it's often better to suppress them to protect your sender reputation and ensure your campaigns reach genuinely interested recipients.
Segment your audience
Divide your email list into segments based on their engagement with your emails, such as recent opens, clicks, or purchases. This allows for highly targeted messaging.
Implement re-engagement campaigns
Design specific campaigns for inactive subscribers, offering compelling reasons to re-engage, such as exclusive content or special discounts. Monitor the responses closely.
While direct, cross-sender open activity validation is generally impossible due to privacy, some companies have explored data cooperatives. These are models where participating senders agree to contribute their own first-party engagement data to a shared, anonymized database. In return, they can query the database for insights on email addresses they themselves have contributed, receiving generalized metrics like most recent open, click, and frequency of activity.
One notable example mentioned in industry discussions is Experian's Email Insights (though its current status and widespread usage are not broadly publicized). The key constraint with such cooperatives is that you can typically only gain insights on email addresses you've already added to the database yourself. It's not a tool for discovering new, active emails from the broader internet, but rather for enriching your existing data based on shared, anonymized engagement within the co-op.
Even with data cooperatives, privacy remains a paramount concern. These systems are designed to ensure no direct sharing of raw email addresses or personally identifiable information between senders. The data is anonymized and aggregated, and access is typically restricted to insights derived from your own contributed list. Furthermore, the coverage and effectiveness of such co-ops can vary significantly by region, with better coverage generally found in major markets like the US compared to, for example, the UK or Australia, as indicated by industry experts.
For the majority of email marketers, relying on first-party engagement data combined with robust email validation for syntax and deliverability remains the most practical and privacy-compliant approach to managing email list health.
Views from the trenches
Best practices
Always prioritize first-party engagement data for segmentation and re-engagement strategies.
Regularly clean your email lists to remove inactive or bouncing addresses and reduce blocklist risks.
Implement a clear consent process to ensure subscribers genuinely opt-in to your communications.
Common pitfalls
Attempting to acquire or use third-party open data, which often violates privacy laws.
Relying solely on SMTP server pings for validation, as many providers block these requests.
Neglecting to segment and re-engage inactive subscribers, leading to lower sender reputation.
Expert tips
Focus on building a strong sender reputation through consistent engagement and good list hygiene.
Utilize email verification services to catch invalid or risky addresses before sending.
Invest in tools that provide deep insights into your own campaign performance and subscriber behavior.
Expert view
Expert from Email Geeks says that validating email addresses based on open activity from other senders is generally impossible due to privacy protections.
2021-03-29 - Email Geeks
Marketer view
Marketer from Email Geeks says that such data sharing is intrusive and goes against privacy safeguards, data protection, and zero/first-party data principles.
2021-03-29 - Email Geeks
Navigating email list health effectively
While the desire to validate email addresses based on open activity from other senders is a common aspiration for marketers seeking to refine their outreach, it's a capability that does not align with modern email privacy standards and technical realities. Mailbox providers do not share this sensitive user data, and attempting to acquire it would likely infringe upon privacy regulations.
Instead of chasing unobtainable cross-sender open data, focus on robust email validation practices and leveraging your own first-party engagement metrics. These are the most accurate and compliant indicators of a subscriber's interest in *your* content. By segmenting your audience based on their direct interactions with your brand and implementing targeted re-engagement campaigns, you can effectively cleanse your lists and improve overall deliverability without compromising privacy.
Prioritizing your owned engagement data and maintaining consistent list hygiene will yield far greater returns in terms of deliverability and campaign effectiveness than searching for an elusive, privacy-violating solution.
Google or 
Microsoft, do not share their users' aggregate or individual open activity with third parties, including other email senders. This would be a massive breach of user privacy and a violation of data protection regulations such as GDPR and CCPA. Their primary responsibility is to protect their users' data, not to facilitate cross-sender engagement tracking. Even Google states that it cannot verify the accuracy of open rates reported by third parties. You can read more about this in their email sender guidelines.
Experian's Email Insights (though its current status and widespread usage are not broadly publicized). The key constraint with such cooperatives is that you can typically only gain insights on email addresses you've already added to the database yourself. It's not a tool for discovering new, active emails from the broader internet, but rather for enriching your existing data based on shared, anonymized engagement within the co-op.
