What types of email bounces should be eliminated and which should be monitored?
Michael Ko
Co-founder & CEO, Suped
Published 28 May 2025
Updated 15 Aug 2025
6 min read
Email bounces are an inevitable part of sending emails, whether you're managing marketing campaigns, transactional notifications, or internal communications. When an email bounces, it means it couldn't be delivered to the recipient's inbox. Understanding the different types of bounces is crucial for maintaining a healthy sender reputation and ensuring your messages reach their intended audience.
Not all bounces are created equal. Some indicate permanent problems with an email address, while others point to temporary issues that might resolve on their own. Knowing which bounces to eliminate immediately and which to monitor can significantly impact your email deliverability and overall campaign success.
Understanding hard bounces and their impact
Hard bounces are permanent delivery failures, meaning the email address is invalid and the message will never be delivered. These occur for several reasons, such as a non-existent email address, a misspelled domain, or a recipient's server permanently blocking your emails.
When an email results in a hard bounce, it's a clear signal that the address is no longer viable. Continuing to send emails to such addresses can severely damage your sender reputation. Internet Service Providers (ISPs) view a high hard bounce rate as a sign of a poorly maintained list or even spamming behavior, which can lead to your emails being flagged or your domain being blocklisted (or blacklisted).
Therefore, hard bounces should be immediately removed from your email lists. This practice is essential for maintaining good list hygiene and protecting your sender reputation. Automated systems in email service providers (ESPs) usually handle this suppression automatically after the first hard bounce.
Hard bounce action
Hard bounces indicate a permanent issue. They should be eliminated immediately from your mailing list to prevent further damage to your sender reputation. Repeatedly sending to invalid addresses signals poor list management to ISPs and blocklist operators.
Managing soft bounces for optimal deliverability
Soft bounces, on the other hand, are temporary delivery failures. These can occur for various reasons, such as a recipient's inbox being full, the server being temporarily unavailable, or the email message being too large. Unlike hard bounces, soft bounces suggest that the email address is valid, and the delivery issue might resolve itself over time.
While a single soft bounce doesn't directly harm your sender reputation as much as a hard bounce, a pattern of continuous soft bounces to the same address can be problematic. It indicates that the recipient is not actively receiving your emails, potentially due to an abandoned inbox or persistent server issues. For more details, explore the differences between soft and hard bounces.
The key with soft bounces is to monitor them. Most ESPs have a built-in mechanism to reattempt delivery for a certain period, and if an email consistently soft bounces (e.g., 3-7 times), the address will eventually be treated as a hard bounce and suppressed. This is a crucial aspect of soft bounce suppression logic that helps protect your sending infrastructure. You can learn more about how ESPs manage bounce codes and tolerance.
Soft bounce type
Reason
Action
Mailbox full
Recipient's inbox has exceeded its storage limit.
Monitor. Reattempt delivery. Suppress if persistent.
Server unavailable
Recipient's email server is temporarily down or offline.
Monitor. Reattempt delivery. These usually resolve.
Message too large
The email size exceeds the recipient server's limits.
Monitor. Reduce email size for future sends to this user.
Monitor. ESPs usually handle retries automatically.
Block bounces and reputation considerations
Block bounces, sometimes referred to as 'blocked' or 'rejected' bounces, occur when an email server or ISP intentionally blocks your message. This isn't necessarily due to an invalid email address, but rather because your email, sending IP, or domain triggered a spam filter or was flagged by a blocklist (or blacklist).
Common reasons for block bounces include: a high volume of complaints from recipients, being listed on a public or private blacklist, poor email content quality, or a lack of proper email authentication (like SPF, DKIM, or DMARC). You can check your status with a blocklist checker.
Block bounces need to be monitored closely. While they might be temporary (e.g., a short-term block), they often signify underlying issues with your sending practices or reputation that require investigation. For persistent block bounces, you should analyze the bounce messages, identify the cause, and take corrective action, which might include delisting requests or improving your email content and sending practices.
Block bounces (spam filters, blacklists)
Cause: Recipient server (or its filters) actively rejects the email.
Examples: Spam filter, IP or domain blacklisted, sender reputation issues.
Action required
Monitor closely. Investigate root cause. Correct issues like poor content, blacklist presence, or authentication failures. Don't just remove these addresses without investigation.
Soft bounces (temporary issues)
Cause: Temporary, transient delivery problem.
Examples: Full inbox, server downtime, message too large.
Action required
Monitor. Allow ESP to reattempt delivery. Suppress only after multiple consecutive failures. Address list hygiene for recurring issues.
Strategies for effective bounce management
Effective bounce management goes beyond simply reacting to bounce messages. It involves proactive strategies to prevent bounces and improve your overall email deliverability. The foundation lies in maintaining a clean and engaged email list.
Regularly validate your email lists to catch invalid addresses before you even send to them. This can significantly reduce hard bounce rates. Additionally, encourage engagement with your emails, as active subscribers are less likely to lead to soft bounces or spam complaints. A low bounce rate is a strong indicator of a healthy, permission-based list, as highlighted by Campaign Monitor's insights.
For soft bounces, it's wise to set up a suppression threshold. If an address soft bounces multiple times over a certain period (e.g., three to five consecutive bounces within a week), consider it a hard bounce and remove it. This prevents you from endlessly trying to reach an inactive or problematic recipient, which can negatively impact your sender reputation over time.
Key strategies
List hygiene: Regularly clean your email lists to remove inactive or invalid addresses. Use email verification services to reduce hard bounces.
Engagement monitoring: Segment your list based on engagement and consider suppressing non-engagers.
Consistent monitoring: Keep a close eye on your bounce rate metrics and act on trends.
Views from the trenches
Best practices
Implement a clear bounce handling policy for your organization, considering factors like email volume and technical capabilities.
Regularly review bounce classifications provided by your ESP and understand what each means for your specific sending.
Utilize email validation services to clean lists proactively, reducing hard bounces before they even occur.
Segment your audience by engagement to identify and manage less active subscribers who might contribute to soft bounces.
Common pitfalls
Removing all bounced emails indiscriminately, which can lead to losing valuable, temporarily undeliverable contacts.
Ignoring soft bounces, allowing them to accumulate and eventually impact your sender reputation negatively.
Not understanding the underlying causes of block bounces, leading to recurring issues with ISPs and blocklists.
Failing to implement a consistent email list hygiene routine, resulting in higher bounce rates over time.
Expert tips
For network or configuration related bounces, investigate potential fixes before immediately removing the addresses.
Use email hygiene and content engagement metrics to decide which valid bounces to restore, update, or archive.
A balanced approach to bounce management can restore over 60% of bounced emails, leading to significant new revenue opportunities.
Monitor soft bounces closely and only suppress addresses that repeatedly bounce over several weeks, typically one to three months.
Expert view
Expert from Email Geeks says bounce handling policies are organization specific, very subjective and depend on many factors, including volume, resource, and technical capabilities.
May 21, 2020 - Email Geeks
Expert view
Expert from Email Geeks says bounce classifications are generally reported as hard, soft, or block, though some ESPs only use soft or hard categories.
May 29, 2020 - Email Geeks
Navigating the bounce landscape
Effective bounce management is not a one-size-fits-all solution. It requires a nuanced understanding of different bounce types and their underlying causes. Hard bounces (permanent failures) demand immediate removal to safeguard your sender reputation and maintain a clean email list. This proactive approach ensures you're not wasting resources on invalid addresses and avoids triggering spam filters.
Soft bounces (temporary failures) and block bounces (rejections due to filtering or reputation) require careful monitoring. They signal issues that might be temporary or indicate deeper problems with your sending practices or domain reputation. By analyzing these bounces, you can identify trends, troubleshoot deliverability issues, and make informed decisions about whether to retry delivery, adjust your content, or suppress an address after repeated failures.
