Why does an email bounce after being opened multiple times?
Michael Ko
Co-founder & CEO, Suped
Published 26 May 2025
Updated 16 Aug 2025
8 min read
It can be incredibly confusing to see an email bounce after your analytics show it has been opened, sometimes even multiple times. This scenario seems contradictory at first glance. If someone opened your email, it means it was delivered, right? Not necessarily. This paradox highlights a common misunderstanding of how email opens are tracked versus how email delivery is finalized.The discrepancy often arises from the technical processes involved in email security and the way engagement metrics are recorded.
Understanding this phenomenon is crucial for accurate deliverability analysis and maintaining a healthy sender reputation. Let's delve into why this happens and what it means for your email campaigns.
Understanding email opens and bounces
Email "opens" are typically tracked using a small, invisible tracking pixel (a 1x1 pixel image) embedded in the email content. When an email client displays the message, it attempts to load this image from your email service provider's server. This action is then registered as an "open."
However, many modern email security systems, spam filters, and antivirus software perform automated scans of incoming emails before they are fully delivered to the recipient's inbox. These scans often involve downloading all assets, including tracking pixels, to check for malicious content, phishing attempts, or suspicious links. This pre-delivery scan triggers the "open" event, even if the email is subsequently rejected and bounces.
There are two main types of bounces: soft bounces and hard bounces. A soft bounce indicates a temporary delivery issue, such as a full mailbox, an offline server, or the message being too large. A hard bounce signifies a permanent failure, like an invalid or non-existent email address. Soft bounces are usually retried by the sending server, but if the issue persists, they can eventually convert into a hard bounce.
The seemingly paradoxical event of an open followed by a bounce often points to a delayed rejection. This means the initial interaction, which triggers the open tracking, occurs before the receiving mail server makes its final delivery decision.
Common scenarios for post-open bounces
One of the most common reasons for a post-open bounce is security scanning. Corporate email servers and advanced security solutions employ sophisticated filters that rigorously scan inbound emails for threats. This includes checking links, attachments, and content for malware or phishing attempts. During this automated scanning process, the email's tracking pixel is often loaded, registering an open, even if the email is ultimately flagged as suspicious and bounced back to the sender.
Another factor is temporary server issues. An email server might initially accept a message and trigger an open, but then encounter a temporary problem that prevents final delivery to the recipient's specific inbox. This could be due to the recipient's mailbox being full, the server being temporarily overloaded, or undergoing maintenance. These issues typically result in a soft bounce. If the problem persists through retries, it could eventually be converted to a hard bounce, while the initial open remains recorded. We have an article that covers why you might see bounces for mailbox full followed by opens, which is a similar scenario.
Some mail servers employ greylisting, which temporarily rejects emails from unknown senders and asks the sending server to retry. During this initial rejection or subsequent retry phase, the content might be fully analyzed. If the email is then deemed problematic upon deeper inspection, it could be bounced even after some assets (like the tracking pixel) were loaded. You can learn more about understanding email greylisting and how it works.
Open tracking logic
Email opens are usually detected when a tiny, invisible image (the tracking pixel) in your email is downloaded. This happens when the recipient's email client or a security system renders the email content. Crucially, this can occur even if the email has not yet been accepted for final delivery into the recipient's personal inbox.
Automated scanning: Mail server security systems download assets for content inspection, triggering an open.
Pre-delivery rendering: The email client or preview pane renders the content, loading the pixel, before a final delivery decision.
Delivery status
An email is considered successfully delivered when the recipient's mail server fully accepts it into the user's mailbox. Bounces occur when the server rejects the email, either temporarily (soft bounce) or permanently (hard bounce), and sends a notification back to the sender.
Delayed rejection: The server might perform deeper content analysis or encounter an issue after the initial acceptance.
Manual actions: A human recipient or admin might manually block or reject an email after viewing it.
Mail server behaviors and rejections
Different email providers have varying protocols for processing incoming mail. Some providers, like Yahoo, might accept the entire message for processing, including all its content and links, before ultimately deciding to reject it. This could happen even if the recipient's email address is invalid. In such cases, the tracking pixel loads, an "open" is recorded, but a hard bounce is generated once Yahoo completes its internal checks. We have a guide that covers the blocklists Yahoo Mail uses.
Spam filters (and blacklists) can also contribute to this phenomenon. An email might initially pass preliminary checks and be delivered to a temporary queue or even a spam folder, triggering the open pixel. However, if the email then undergoes more stringent analysis and is found to contain characteristics of spam, it could be rejected by the server, resulting in a bounce. This means the email might be treated as a soft bounce initially, then become a hard bounce if repeated attempts to deliver fail due to its spam classification. You can read more about soft bounces and how to fix them here. To gain a deeper understanding, review how email blacklists actually work.
In some cases, the recipient or their IT administrator might manually block your sender after viewing the email. If the email initially made it past the basic security layers to a point where it could be opened (or its pixel loaded by a security scanner), a manual block or rejection initiated by the recipient could then trigger a bounce notification back to your sending system.
Impact on sender reputation and troubleshooting
While an open followed by a bounce can be a nuanced issue, it's still crucial to address. High bounce rates, regardless of prior engagement, negatively impact your sender reputation with ISPs. This can lead to your emails being directed to the spam folder or outright blocked in the future, even for valid recipients.
To troubleshoot these occurrences, start by examining the detailed bounce codes provided by your email service provider. These codes often offer specific reasons for the rejection. Check your email bounce messages. Pay close attention to mail transfer agent (MTA) logs, as they can reveal the exact sequence of events, including temporary failures or delayed rejections after content scanning. If you notice a pattern with certain domains, investigate their specific filtering policies.
Maintaining a clean and engaged email list is your best defense. Regularly remove hard-bounced addresses from your lists, as they are permanently undeliverable. For soft bounces, monitor patterns and consider temporarily suppressing recipients who consistently soft bounce before removing them entirely. Also, ensure your domain isn't on any major blocklists or blacklists, which can lead to widespread delivery issues. We offer blocklist monitoring to help you stay informed.
Actionable steps for resolution
Analyze bounce reasons: Review bounce codes and MTA logs for specific rejection details.
Maintain list hygiene: Regularly remove hard bounces and manage persistent soft bounces.
Monitor sender reputation: Keep an eye on your domain and IP health, checking for blocklist entries.
Strengthen authentication: Ensure proper SPF, DKIM, and DMARC records are in place to build trust.
Views from the trenches
Best practices
Monitor email engagement closely, but be aware of how 'opens' are tracked versus actual delivery.
Regularly clean your email lists to remove invalid addresses and those that consistently soft bounce.
Implement strong email authentication (SPF, DKIM, DMARC) to build trust with receiving servers.
Common pitfalls
Mistaking pixel loads for genuine human opens, especially from security scanners.
Ignoring soft bounces, which can eventually turn into hard bounces and impact reputation.
Failing to investigate the underlying reasons for bounces, leading to recurring issues.
Expert tips
"Some email providers, like Yahoo, accept the full message before rejecting it, which can explain the 'open' before a hard bounce." – tvjames
"Detailed MTA logs are crucial. They can show if an email was greylisted or if filters reviewed content post-initial attempt." – aiverson
"Always remember that 'open' metrics are asset downloads, not necessarily human interaction, especially with automated systems." – marcel.beckers
Expert view
Expert from Email Geeks says: You are often not measuring true 'opens' but rather asset downloads by automated systems like security scanners, which occurs before final delivery.
2023-07-13 - Email Geeks
Expert view
Expert from Email Geeks says: Some company filtering layers can allow an email to be viewed or clicked within their system before it is subsequently bounced back to the sender.
2023-07-13 - Email Geeks
Resolving the bounce paradox
The phenomenon of an email bouncing after being opened multiple times is a common head-scratcher for marketers, but it has logical explanations rooted in email infrastructure and security practices. It's not a true contradiction but rather a timing discrepancy between how opens are tracked (via pixel loads) and the final delivery decision made by receiving mail servers.
Automated security scans, temporary server issues, and specific mail server behaviors (like delayed content analysis or greylisting) are primary culprits. These processes can trigger an open event by downloading email assets before deciding to reject the email, resulting in a bounce notification. It's a reminder that a pixel load doesn't always equate to successful inbox placement and human engagement.
By understanding these nuances and implementing robust email deliverability best practices, such as rigorous list hygiene and careful monitoring of bounce reasons, you can better interpret your campaign data and improve overall email performance. This deeper insight allows you to distinguish between genuine engagement and automated system interactions, leading to more accurate reporting and better strategic decisions for your email program.
Yahoo, might accept the entire message for processing, including all its content and links, before ultimately deciding to reject it. This could happen even if the recipient's email address is invalid. In such cases, the tracking pixel loads, an "open" is recorded, but a hard bounce is generated once Yahoo completes its internal checks. We have a guide that covers the blocklists Yahoo Mail uses.
