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Email marketing can be a powerful tool for businesses to reach customers and drive engagement. However, not all email campaigns go as planned. One common issue that arises is bounced emails – when an email is undeliverable and gets sent back to the sender. 

Bounced emails can negatively impact deliverability rates and cost businesses money in wasted marketing spend. That’s why it’s critical to understand the different types of email bounces, namely hard bounces and soft bounces. 

In this article, we look at ways to properly diagnose email bounce issues and take corrective actions to improve campaign performance over time. 

Email Bounces: An Overview

An email bounce occurs when an email is undeliverable and gets sent back or “bounces” to the original sender. This happens for various reasons such as an invalid email address or a recipient’s inbox being full. Simply put, a bounce means the intended recipient did not receive the email message.

There are two main categories of email bounces: 

  1. Hard bounces – These are permanent failures, meaning that a particular email address is invalid and will never receive messages. 
  1. Soft bounces – These are temporary failures that occur due to temporary issues like a full inbox or email server being down.


The key difference lies in the permanence of the bounce. With hard bounces, the email address is deemed undeliverable so all future messages will continue bouncing. Soft bounces indicate a temporary delivery failure, so emails may still reach the recipient once the problem is resolved. 

Understanding this distinction is important for email marketers when diagnosing issues and determining the next steps.

Understanding Soft Bounces

A soft bounce is defined as a temporary email delivery failure that occurs when an intended recipient’s email address is valid, but the message cannot be delivered due to a temporary issue. 

Soft bounces indicate the recipient’s mailbox is active and functional, but some obstruction is temporarily blocking the email from going through successfully.

Some characteristics of soft bounces include error messages that indicate a temporary failure, bounce codes starting with 4 or 5, and the original email remaining on the sender’s email servers instead of being deleted. 

Soft bounces essentially mean “try again later” rather than a permanent failure. Several common causes lead to soft bounces materializing. 

Causes of Soft Bounces

Cause #1: Technical Issues: The first is temporary and intermittent issues with the recipient’s email system, server, or network connection. 

Things like maintenance downtime, traffic spikes, and software glitches can all force recipient servers to soft bounce messages. As soon as the issue is resolved on their end, messages will start flowing through.

Cause #2: Full Inbox: Another frequent cause is the recipient’s mailbox being too full. Every email account has storage limits in place by providers. When inboxes reach maximum capacity, new incoming messages bounce back softly. 

Recipients must manually delete emails and free up space before deliveries can recommence. This indicates the address itself is fine, but the inbox is too cluttered.

Cause #3: Email Server Configuration: Finally, problems with the configuration of a recipient’s email server itself can also lead to soft bounces. 

Some common examples include security filters flagging emails as spam, greylisting practices deliberately delaying messages to prevent spam or just general software errors. Fine-tuning these systems typically remedies the soft bounce situations resulting from them.

While not permanent like hard bounces, soft bounces should still remain on the radar of email marketers.

High soft bounce rates make it more difficult to achieve strong deliverability and inbox placement. ISPs may start throttling the number of emails received if they see excessive soft bounces. 

Soft bounces also allow marketers to pinpoint potential issues with their contact lists and troubleshoot before the problems worsen. With some attention and effort, the causes of soft bounces can usually be corrected.

Impact of Soft Bounces on Email Deliverability

A high volume of soft bounces can detrimentally impact a sender’s reputation with major email service providers like Gmail and Yahoo. 

These companies closely monitor bounce rates and may interpret a flood of soft bounces as a sign that the sender has list quality issues, many inactive subscriber addresses, or poor deliverability practices. 

If too many soft bounces occur, the sender’s domain could get labeled as an “unreliable” or even high-risk sender by these major email providers. This classification can lead to throttled send rates, spam folder routing, or even potential blocking for future email campaigns. Clearly, excessive soft bounces raise red flags.


Also, all of those soft-bounced messages occupying bandwidth also contribute directly to email deliverability struggles. 

As more emails get turned away with temporary soft bounces instead of landing in subscriber inboxes, the overall email deliverability rate declines. Open rates, click-through rates, and other engagement metrics also decrease without successful message delivery. 

Recipients can’t open an email they never received due to soft bouncing. The underlying issues causing the bounces must be addressed to increase the volume of emails actually arriving and being read.

Marketers should be proactive with several techniques to maximize deliverability rates and reduce soft bounces. 

  • Firstly, subscriber lists should be closely monitored and maintained by removing inactive email addresses or contacts that have not engaged recently. 
  • Double opt-in confirmation processes should be used when subscribers sign up to validate email accuracy. 
  • Soft bounces themselves should be tracked by subscribers so follow-ups can uncover the root causes. Recently bounced addresses can be temporarily suppressed from sends until the issue is resolved. 
  • Carefully crafted subject lines and email content can avoid common spam trigger words. For more persistent problems, the recipient’s ISP may need to be contacted directly to whitelist the sender’s IP address. 

With vigilance and care, soft bounce rates can be minimized to protect the sender’s reputation and boost inbox placement.

Differentiating Soft Bounces from Hard Bounces

The main difference lies in the permanence of the failure – soft bounces are temporary while hard bounces indicate unfixable issues. 

Soft bounces have error messages indicating a transient failure and the email stays on the sending server. Hard bounces mean the message is deleted from the sender’s system.

Senders should track bounce rates over time and by subscriber. A pattern of repetitive soft bounces for a recipient indicates a persistent problem requiring troubleshooting. Isolated soft bounces are less concerning than a high overall bounce rate. Hard bounces merit immediate removal of those addresses.

A “mailbox full” error for a subscriber is a soft bounce that may resolve after the person cleans up their overflowing inbox. An invalid mailbox response is a hard bounce for an inactive address – that recipient will never receive emails. Noticing subtle differences helps diagnose issues.

While easy to confuse at first, soft and hard bounces reveal very different insights about email campaign health and opportunities for improvement. 

Reducing Soft Bounces in Email Campaigns

Here are several best practices that can reduce soft bounces:

  1. Use double opt-in sign-up flows to confirm addresses. Validating and keeping email lists clean is crucial. 
  2. Ensure subject lines aren’t flagged as spam. 
  3. Segment contacts by engagement. Segmentation and targeted messaging ensure subscribers get the content they want to open.  
  4. Keep a tight focus on qualified, engaged contacts, and temporarily remove inactive subscribers. You can also periodically re-engage subscribers to confirm opt-ins. 
  5. Monitor soft bounces closely to identify and troubleshoot root causes. 
  6. Contact recipients or ISPs when needed.
  7. Remove hard bounces immediately and soft bounces after follow-up. 
  8. Avoid purchasing generic email lists which may contain many invalid addresses. 

Separate engaged subscribers from inactive contacts sending mainly promotions or newsletters. Customize messaging to subscriber preferences for higher open rates. Serve varied content that is relevant and valuable.

Proactively minimizing soft bounces through validation, list management, and segmentation will build the sender’s reputation and boost campaign performance over time. Please let me know if you need any part expanded further!

Addressing Soft Bounces

When soft bounces occur, marketers should implement a systematic process for diagnosing, troubleshooting and addressing the root causes to resolve deliverability issues. 

The first step is carefully analyzing the soft bounce error messages and codes to identify potential reasons why the email could not be delivered successfully. 

Check factors like 

  • Recipient inboxes being over capacity
  • Inactive or invalid addresses
  • Accidental spam filter flagging
  • Deactivated account links
  • Email content formatting 

These are all areas that could trigger a soft bounce. Thoroughly investigating these variables enables marketers to pinpoint the true underlying source of the problem.

Once the cause is determined, appropriate corrections can be made before retrying message delivery. 

For soft bounces due to full inboxes or server outages, temporarily waiting and resending the email again soon is often effective. Recipient servers tend to recover quickly from temporary glitches, so a well-timed retry attempt maximizes the chances of successful delivery with the soft bounce issue eliminated. 

However, marketers should be careful not to retry the same message over and over, as this can inadvertently worsen deliverability.

In the case of recurring soft bounces for the same recipients, more extensive troubleshooting and re-engagement are required. 

These contacts should be added to suppression lists to pause further campaign emails temporarily until the problem is solved. Marketers should then reach out to these subscribers to confirm the accuracy of their addresses and re-permit future communications. 

Sometimes re-opting solves recurrent soft bouncing issues. For unresponsive recipients, removing them from contact lists altogether may be prudent to avoid harming the sender reputation.

Carefully diagnosing, following up on, and addressing both individual and widespread soft bounces is crucial for improving email deliverability over time. With a thoughtful process to tackle soft-bounce problems, marketers can turn initial delivery failures into future email marketing success.

Tools and Resources for Managing Soft Bounces

Email marketing platforms like Mailchimp, Constant Contact, and AWeber include built-in soft bounce tracking and notification functions. 

These tools enable marketers to monitor soft and hard bounce rates for each campaign, segment subscriber lists based on bounce activity, and configure automated list-cleaning routines to remove bounced addresses.

Specialized third-party tools like SendGrid, Listrak, and Electric Mail offer advanced bounce processing features and detailed analytics for diagnosing delivery issues. For example, SendGrid’s Soft Bounce Blocker tool automatically suppresses subscriber addresses after three consecutive soft bounces, helping improve future deliverability.

Brands like Netflix have implemented rigorous workflows to address subscriber soft bounces. Netflix uses re-engagement emails customized for soft-bounced subscribers and has routines in place to eventually remove non-responsive contacts after multiple failed contact attempts. 


In email marketing, not all bounces are created equal. While permanent hard bounces reveal address errors, temporary soft bounces signal opportunities to improve deliverability when properly addressed. 

A solid foundation on bounce management paves the way for more effective email marketing. Use the information in this guide to equip yourself with the tools and knowledge to minimize soft bounces so you can send bounce-free emails that consistently land in subscriber inboxes.

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