Is it bad to email addresses that keep soft bouncing?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 Jun 2025
Updated 16 Aug 2025
8 min read
Email soft bounces are often seen as temporary hiccups, a brief pause in delivery that will resolve itself. An inbox might be full, or a recipient's server could be temporarily offline, leading to a 4xx SMTP error code indicating a transient issue. Because they're not permanent, many email marketers don't give them much thought, especially if their email service provider (ESP) re-queues and retries delivery for a period.
However, the real question arises when an email address keeps soft bouncing on successive sends. Is it truly harmless to continue emailing such an address? I've seen firsthand how a lack of proper soft bounce management can subtly, but significantly, degrade email deliverability and sender reputation over time. It's a nuanced problem that deserves careful attention to maintain a healthy email program.
What is a soft bounce?
A soft bounce indicates a temporary delivery issue. This means the email address is valid, and your message reached the recipient's mail server, but it couldn't be delivered for a specific, non-permanent reason. Common scenarios include a recipient's mailbox being full, the receiving server experiencing a temporary outage, or the message being too large. Your ESP will typically attempt to resend these emails over a period, often up to 72 hours, before marking them as a soft bounce.
In contrast, a hard bounce signifies a permanent delivery failure, meaning the email cannot be delivered under any circumstances. This usually happens when the email address is invalid, non-existent, or the recipient's server has permanently blocked delivery. Unlike soft bounces, hard bounces (indicated by 5xx SMTP errors) should result in immediate suppression of the address from your list, as continuing to send to them is severely detrimental to your sender reputation. For more details on this distinction, you can explore our guide on hard and soft bounces.
Understanding these differences is crucial for effective email list management. While some ESPs may automatically handle re-tries for soft bounces, it's important to know their policies and how they impact successive sends to the same address over time. Not all soft bounce types are created equal, and some, like reputation blocks, might indicate underlying issues that require closer inspection.
Soft bounces
Soft bounces occur due to temporary issues. The email address is valid, but the message couldn't be delivered at that moment. Reasons include a full inbox, a temporary server issue, or the message size exceeding limits. ESPs typically retry these sends, and the issue may resolve itself.
They often use 4xx SMTP error codes.
Hard bounces
Hard bounces are permanent delivery failures. This means the email address is invalid, non-existent, or the domain is incorrect. There's no point in retrying these, as they will never be delivered. Continued sending to hard bounces severely damages sender reputation.
They typically result in 5xx SMTP error codes.
The subtle dangers of persistent soft bounces
While an occasional soft bounce is normal, allowing addresses to repeatedly soft bounce can have a detrimental impact on your sender reputation. Internet Service Providers (ISPs) and mailbox providers (like Google and Yahoo) monitor bounce rates closely as an indicator of list quality. A consistent pattern of soft bounces signals that your list might be stale, poorly maintained, or that you're sending to unengaged recipients, even if the address itself is technically valid.
This can lead to a gradual erosion of your sender score and increase the likelihood of your emails being sent to the spam folder, or even worse, being outright blocked. As Braze points out, repeated soft bounces to the same email addresses can gradually harm your sender reputation. Additionally, an abandoned mailbox that consistently soft bounces might eventually be converted into a spam trap, which can lead to severe blocklist (or blacklist) penalties.
Essentially, while a single soft bounce might be a blip, a pattern of them paints a picture of poor list hygiene and potentially unwanted mail, which can lead to higher spam complaint rates, lower engagement, and ultimately, a reduced deliverability rate. Even if your ESP continues to send, the impact on your domain and IP reputation can be significant.
Ignoring persistent soft bounces
Sender reputation decline: ISPs see repeated bounces as a sign of low-quality lists.
Increased spam folder placement: Your emails are more likely to bypass the inbox.
Risk of spam traps: Abandoned addresses can turn into traps, leading to blocklisting.
Wasted sending resources: You're sending emails that won't reach their destination.
Actively managing soft bounces
Improved deliverability: Emails are more likely to land in the inbox.
Enhanced sender reputation: ISPs trust your sending practices more.
Reduced costs: Less money spent on sending to unengaged or unreachable contacts.
Cleaner email list: Focus on engaged and reachable subscribers.
Managing soft bounce thresholds
Many email service providers implement a soft bounce tolerance, a system that automatically suppresses an email address after it has soft bounced a certain number of times over multiple campaigns. For instance, Mailchimp allows up to seven soft bounces before considering the address invalid. This automated approach is essential for maintaining list hygiene and protecting sender reputation. If your ESP doesn't have such a built-in feature, or if you're experiencing unusually high soft bounce rates, you'll need to implement your own strategy.
Without an automated soft bounce tolerance, you face the challenge of continuously sending to addresses that are unlikely to receive your mail, impacting your overall email deliverability. This can be particularly problematic if different soft bounce types carry different risks. For example, a mailbox full bounce might signal an abandoned address, while a temporary block due to reputation could indicate issues with your sending practices. Each scenario ideally requires a tailored response.
The recommended approach for a robust soft bounce suppression logic involves setting a clear threshold for repeat soft bounces over a defined period. This could mean suppressing an address after three consecutive soft bounces, or after a certain number of soft bounces over a month or quarter, depending on your sending frequency. This proactive management helps to prevent negative impacts on your domain and IP reputation. To understand how such policies affect deliverability, you can read more on soft bounce retry policies.
Soft bounce type
Example SMTP code
Typical cause
Recommended action
Mailbox full
452 4.2.2
Recipient's inbox has reached its storage limit.
Suppress after 2-3 consecutive bounces, as it may indicate an abandoned mailbox.
Server unavailable/timeout
421, 451
Recipient's server is temporarily down or overloaded.
Allow ESP to retry; if persistent, monitor the domain or suppress.
Message too large
552 (often with 4xx variants)
The email content exceeds the recipient's server size limits.
Review email content for large attachments; suppress if not fixable.
Reputation block
421 4.7.1
Temporary block due to suspicious sending patterns or content.
Investigate sender reputation and content; suppress if issue persists.
Implementing an effective bounce management strategy
The most effective way to mitigate the risks of persistent soft bounces is through proactive and rigorous list hygiene. This means regularly reviewing your email list and taking action on addresses that show a pattern of soft bouncing. If your ESP doesn't automate this, you might need to implement a manual process, such as exporting bounce reports, identifying repeat offenders, and then suppressing or removing those contacts from your active mailing lists. This manual intervention, while demanding, is critical.
Consider implementing a sunset policy, not just for unengaged recipients, but specifically for those who consistently soft bounce. A sunset policy ensures that you're removing contacts who are not opening or clicking your emails, regardless of bounce status. For addresses that consistently soft bounce due to full mailboxes or other temporary issues, it's often best practice to suppress them after a few attempts. You can learn more about cleaning up soft bounces for better deliverability.
By proactively managing soft bounces, you demonstrate to ISPs that you maintain a healthy, engaged email list. This, in turn, can significantly improve your inbox placement and overall sender reputation, helping you avoid being placed on a blocklist (or blacklist). The goal is to focus your efforts on reaching active and engaged subscribers, maximizing the return on your email marketing investments.
Key actions for healthy lists
Automate suppression: Configure your ESP to automatically suppress addresses after a defined soft bounce threshold.
Monitor bounce reports: Pay attention to patterns and types of soft bounces to identify underlying issues.
Validate new addresses: Use real-time verification to prevent invalid addresses from entering your list.
Views from the trenches
Best practices
Implement a clear soft bounce suppression policy within your email marketing platform.
Regularly review and clean your email lists to remove persistently bouncing addresses.
Define a reasonable soft bounce tolerance for your specific sending frequency and audience.
Use engagement metrics in conjunction with bounce data to identify inactive subscribers.
Common pitfalls
Assuming soft bounces are always harmless and will resolve themselves over time.
Relying solely on your ESP's default bounce handling without understanding its specifics.
Failing to manually manage soft bounces if your platform lacks advanced automation features.
Not differentiating between various soft bounce types, like temporary server issues versus full mailboxes.
Expert tips
Consider a sunset policy to remove unengaged recipients and those consistently soft bouncing.
Analyze bounce data to identify issues at the source, such as poor data collection practices.
Suppress soft bounces after multiple failures over weeks, especially without user activity.
Be prepared to manually export and manage bounce lists if your ESP automation is limited.
Expert view
Expert from Email Geeks says: ESPs generally queue a soft bounced message for retry, and eventually, the message will permanently fail if delivery isn't possible.
2021-07-08 - Email Geeks
Expert view
Expert from Email Geeks says: The type of soft bounce matters; a temporary timeout is different from a persistent block due to abuse.
2021-07-08 - Email Geeks
Securing your sender reputation
Emailing addresses that continually soft bounce is indeed detrimental to your email program. While individual soft bounces are temporary, a consistent pattern indicates underlying issues that can erode your sender reputation, increase spam folder placement, and even lead to blocklisting (or blacklisting). Ignoring these signals can silently undermine your email deliverability efforts, making it harder for your legitimate messages to reach their intended recipients.
Proactive management of soft bounces, whether through automated ESP features or diligent manual processes, is not merely a technicality; it's a fundamental aspect of maintaining a healthy and effective email marketing strategy. By cleaning your lists, setting appropriate bounce tolerances, and addressing the root causes of persistent soft bounces, you safeguard your sender reputation and ensure your valuable content consistently reaches the inbox.
Google and 
Yahoo) monitor bounce rates closely as an indicator of list quality. A consistent pattern of soft bounces signals that your list might be stale, poorly maintained, or that you're sending to unengaged recipients, even if the address itself is technically valid.
