Why are emails hard bouncing then opening and clicking links later?
Michael Ko
Co-founder & CEO, Suped
Published 27 May 2025
Updated 16 Aug 2025
7 min read
Email deliverability can be perplexing, and few scenarios are as baffling as seeing an email hard bounce, only for it to register an open or even a click days later. This situation contradicts the fundamental understanding of a hard bounce, which typically signifies a permanent delivery failure. It raises crucial questions about reporting accuracy, the behavior of recipient systems, and the true status of your email campaigns.
The confusion stems from the expectation that once an email hard bounces, it means the recipient's email address is invalid or no longer exists. Common reasons include typos, defunct addresses, or outright fake accounts. In such cases, the email should not, in theory, be opened or interacted with by any legitimate recipient.
However, the reality of complex email ecosystems, involving various security layers and reporting mechanisms, can lead to these seemingly contradictory outcomes. Understanding the underlying causes is essential for maintaining a healthy sender reputation and ensuring your email marketing efforts are based on accurate data.
Understanding hard bounces and delivery states
A hard bounce fundamentally indicates a permanent delivery failure. This means the recipient server has informed the sending server that the email cannot be delivered for a permanent reason. Typical examples include a nonexistent mailbox (e.g., 550 5.1.1 User unknown) or a domain that doesn't exist. Once an email hard bounces, the address should ideally be removed from your active mailing list to protect your sender reputation and avoid future delivery issues.
Contrast this with a soft bounce, which is a temporary delivery issue, such as a full mailbox or a temporarily unavailable server. Soft bounces are usually retried by the sending server, and the email might eventually be delivered. The distinction between hard and soft bounces is critical for proper list hygiene, as outlined in guides like the difference between soft and hard bounces.
When a hard bounce occurs, the expectation is that the email simply didn't reach its intended destination. The appearance of opens and clicks after a hard bounce suggests an anomaly in the reporting, the mail flow, or the interaction of automated systems. This is particularly puzzling because an interaction, such as an open or click, typically means the email was successfully delivered and rendered, even if only by a machine.
The role of security filters and scanners
One of the most common explanations for this phenomenon involves recipient-side security filters. Many modern email systems, especially those protecting corporate networks, use advanced security solutions that scan incoming emails for malicious content before actual delivery. These scanners may open emails, click links, and even load tracking pixels in a sandbox environment to evaluate potential threats.
This automated scanning can register as an open or click in your email marketing platform's analytics, even if the email is subsequently rejected and hard bounces. This is often referred to as an asynchronous bounce, where the bounce message is generated after the initial delivery attempt appeared successful. These systems might perform their checks after the initial SMTP DATA command, only to issue a 4xx (temporary) or 5xx (permanent) rejection response later.
Furthermore, some filters might initially accept the email, scan it, and then, based on the scan results, reject it or move it to a spam folder. If your email platform records the open or click from the scanner before the final rejection message is processed, it leads to this confusing reporting. This behavior can also be observed with hidden links in emails, where bots generate high click rates, as discussed in why hidden links get high click rates.
How automated scanning affects metrics
Automated security scanners, such as those used by Gmail and Office 365, are designed to protect users from phishing, malware, and spam. They achieve this by pre-fetching email content and scanning embedded links and images.
This pre-fetching activity, while beneficial for security, can inadvertently trigger tracking pixels and redirect links, leading to recorded opens and clicks, even when the email itself ultimately bounces. It's a common reason why you might see artificial email opens and clicks reported.
Misreporting by email service providers
Another significant factor contributing to this confusion can be the way email service providers (ESPs) handle and report bounces. Not all ESPs categorize bounces in the same manner, and some might have delays in processing bounce notifications or associating them with recipient activity.
For instance, an ESP might initially record an email as delivered, then later receive a hard bounce notification. If a security scanner or bot interacted with the email during the interim period, the ESP's reporting system might incorrectly attribute the open or click to the email address before the bounce was fully processed. This can lead to a situation where a bounced email appears to have been engaged with.
Additionally, issues with variable envelope return path (VERP) addresses, which are used to track bounces, could lead to miscategorization. If spam or other irrelevant mail is sent to these VERP addresses, some sending platforms might incorrectly categorize it as a hard bounce from a legitimate recipient. This highlights why bounce notifications can differ significantly and sometimes mark bounced emails as read.
Bounce type
SMTP code category
Likely cause
Impact on reporting
Hard bounce
5xx
Permanent failure, e.g., nonexistent address
Should cease sending to this address. Opens/clicks after are anomalies.
Soft bounce
4xx
Temporary issue, e.g., mailbox full, server down
Email may be retried and delivered. Interactions are expected if delivery succeeds.
Asynchronous bounce
4xx or 5xx (delayed)
Recipient server initially accepts then rejects after content scan
Can show opens/clicks from scanners before bounce is recorded. Requires careful analysis.
What to do when you see this happening
When confronted with hard bounces followed by opens or clicks, the first step is to investigate the raw bounce reason codes from your ESP. These codes provide more specific details than a generic hard bounce label. Look for 4xx (temporary failure) or delayed 5xx codes that might indicate a filtering process rather than a truly nonexistent address. This detailed information is crucial for proper email deliverability troubleshooting.
It's also important to review your email list hygiene practices. While these specific bounce scenarios are nuanced, a high volume of hard bounces overall can signal underlying issues with your list acquisition methods. Regularly cleaning your list and promptly removing definitively hard-bounced addresses helps protect your sender reputation from being added to a blocklist (or blacklist), as explained in what happens when your domain is blocklisted. Maintaining a clean list also reduces the risk of hitting spam traps, which can also trigger anomalous behavior and hurt your standing.
Navigating complex email delivery scenarios
When you encounter such anomalies, consider reaching out to your email service provider's support team. They may have access to more granular logging and data, which can shed light on the exact sequence of events, including when the bounce notification was received relative to any recorded opens or clicks. This can help you understand if the bounce is indeed a miscategorization or a result of automated scanning.
Ultimately, focusing on robust email authentication, maintaining a healthy sender reputation, and closely monitoring your deliverability metrics are key to navigating these complex scenarios. While a hard bounce typically means a permanent failure, understanding these edge cases helps you make informed decisions about your email strategy and ensure your messages truly reach their intended audience.
Views from the trenches
Best practices
Always request raw bounce reasons or SMTP codes from your ESP for detailed analysis, beyond simple bounce categories.
Implement a robust list hygiene strategy to regularly identify and remove addresses that consistently hard bounce.
Monitor your engagement metrics in conjunction with bounce reports to identify patterns of artificial opens or clicks from security scanners.
Common pitfalls
Failing to investigate anomalous hard bounces, leading to inaccurate subscriber status or poor sender reputation.
Assuming all reported hard bounces mean a truly dead email address without considering delayed rejections or scanner activity.
Not differentiating between hard and soft bounces, potentially removing valid, temporarily unreachable addresses.
Expert tips
If an email is soft-rejected after DATA, security filters may still trigger opens and clicks from scanning, even if the email is never truly delivered to the inbox.
Some ESPs may miscategorize bounces, especially when dealing with delayed rejections or specific server responses.
Advanced reporting that includes the stage of the SMTP transaction where a rejection occurs (e.g., connect, DATA) would greatly clarify bounce reasons.
Marketer view
Marketer from Email Geeks says they saw a weird situation where hard bounces occurred, but then opens or clicks followed, and even multiple hard bounces over months on the same email address.
2021-12-01 - Email Geeks
Expert view
Expert from Email Geeks says that if these are delayed bounces, clicks and opens might be triggered by content or link scanners.
Gmail and 
Office 365, are designed to protect users from phishing, malware, and spam. They achieve this by pre-fetching email content and scanning embedded links and images.
