Email marketing is one of the most effective tools for building relationships and driving sales, but it comes with its challenges. One of the biggest issues marketers face is dealing with email bounces. These bounces fall into two categories: hard bounces and soft bounces.

Hard bounces result from permanent delivery failures, such as sending to invalid email addresses, while soft bounces indicate temporary issues, like a full inbox or server errors. Left unaddressed, bounces can hurt your sender's reputation, lower your email deliverability, and ultimately impact your campaign’s ROI.

In this guide, we’ll dive into the key differences between hard and soft bounces, their impact on your campaigns, and actionable steps to resolve and prevent them.

Section 1: What Are Hard and Soft Bounces?

Understanding the difference between hard and soft bounces is the first step to managing them effectively. While both indicate that an email wasn’t successfully delivered, the causes and resolutions vary greatly. This section will break down these terms and help you identify how they impact your email campaigns.

Definitions of Hard and Soft Bounces

• Hard Bounce: A permanent delivery failure. This happens when the email address doesn’t exist, is invalid, or the domain is incorrect.
  Example: Sending an email to "john.doe@nonexistentdomain.com" will result in a hard bounce.

• Soft Bounce: A temporary delivery failure. Common reasons include a full inbox, the recipient's server being down, or the email being too large to process.
  Example: If "jane.doe@gmail.com" has a full inbox, your email might bounce temporarily.

  
  

Section 2: Why Hard and Soft Bounces Matter for Email Deliverability

Ignoring email bounces can quickly damage your sender's reputation and reduce the effectiveness of your campaigns. In this section, we’ll explore why hard and soft bounces matter, and how they can affect both your deliverability and overall ROI.

Effects on Sender Reputation

A high bounce rate signals to email providers like Gmail, Outlook, or Yahoo that your emails may be spammy or poorly managed. Address these issues early by reviewing our Email Deliverability Checklist.

• This can result in lower inbox placement rates, pushing more of your emails into spam folders.

• Over time, consistently high bounce rates can lead to blacklisting, severely limiting your ability to reach recipients. Explore Top Email Marketing Mistakes to avoid to prevent common pitfalls.

Email providers evaluate sender reputation based on several factors, and bounces weigh heavily in their scoring systems.

• A poor reputation not only affects the current campaign but also future ones, reducing long-term email marketing success.

Campaign Performance Impacts

Bounces affect key performance metrics such as:

• Open Rates: If your emails aren’t delivered, they can’t be opened, which directly affects your campaign's reach and visibility.

• Engagement Metrics: Bounces lead to lower click-through and conversion rates, making it harder to measure success accurately.

• ROI: High bounce rates reduce the number of potential customers engaging with your offers, directly impacting revenue opportunities.

Section 3: Common Causes of Hard and Soft Bounces

Every bounce has a reason, and understanding these causes is crucial to finding a solution. This section dives into the common reasons behind hard and soft bounces, helping you spot red flags and take proactive measures.

Common Causes for Hard Bounces

1. Invalid Email Addresses: Incorrectly entered or non-existent email addresses. Double opt-ins can prevent this, as explained in our 5 Proven Techniques for Increasing SMS Opt-Ins in Klaviyo.

Source: Kickbox

2. Nonexistent Domains: Emails sent to no longer active or incorrectly formatted domains.

Source: Campaign Monitor

3. Permanently Blocked Addresses: Addresses that have previously unsubscribed, marked emails as spam, or belong to a blocked list.

Example: These are common when sending to outdated lists or ignoring unsubscribed users.

Common Causes for Soft Bounces

1. Full Inboxes: The recipient’s mailbox is full and cannot accept new messages.

Example: A rarely used email account exceeding its storage capacity.

2. Temporary Server Outages: Issues like server downtime or connectivity problems on the recipient’s end.

Example: Often occurs during peak periods or maintenance windows.

3. Large Email Attachments: Emails exceeding the size limits set by email providers.

Example: Promotional emails with oversized images, videos, or attachments that fail to meet provider requirements.

4. High Sending Volumes: Overloading mailbox providers with bulk emails can trigger temporary rejections.

Tip: Address this by implementing batch sending or limiting send volumes to specific domains.

Section 4: How to Minimise Hard and Soft Bounces

Preventing bounces starts with proactive email management strategies. In this section, we’ll cover practical tips and tools you can use to reduce hard and soft bounces, ensuring your campaigns reach their intended audience.

Strategies to Reduce Email Bounces

1. Email List Hygiene

• Regularly clean your email list to remove invalid or outdated addresses using tools like NeverBounce or ZeroBounce. For more advanced strategies, check out 3 Klaviyo Segmentation Strategies to Boost DTC Sales.

• Implement a sunset flow to suppress unengaged recipients before their mailboxes become invalid automatically. This prevents invalid address bounces over time. Klaviyo

  
  

Source: ZeroBounce

2. Enable Double Opt-In

• Double opt-in ensures that all collected email addresses are valid, reducing the risk of invalid or fake addresses entering your list.

• Combine this with regular email validation to maintain a healthy and deliverable list. Klaviyo

  
  

Source: Klaviyo 

3. Monitor and Repair Sender Reputation

• Reputation matters: Regularly monitor key deliverability metrics such as open rates, bounce rates, and spam complaints. Read Klaviyo Predictive Analytics: AI Guide & 3 Use Cases to learn how data can inform your email strategies.

• Tighten sunsetting windows to remove unengaged profiles faster. If necessary, temporarily reduce sending frequency to repair your sender's reputation. Klaviyo

4. Limit Message Length and Size

• Shorter emails are easier to read and less likely to bounce. Limit message scrolling by keeping your content concise.

• Ensure email size is below 110KB, including media files. Oversized emails can cause deliverability issues. Klaviyo

  
  

Source: ReallyGoodEmails

5. Optimise Sending Infrastructure

• If your sending frequency is too high, it can negatively affect deliverability. Warm up your sending infrastructure and gradually increase email volume. Learn how to maintain balance with Klaviyo Smart Sending.

• Use batch sending to spread messages over a longer duration, reducing bounce rates caused by volume overload. Klaviyo

6. Address Technical and Authentication Issues

• Ensure your DNS records, such as SPF, DKIM, and DMARC, are correctly configured to validate your emails.

• If bounces are concentrated on one mailbox provider, investigate for provider-specific issues. Sometimes no action is needed if the problem lies solely with the provider. Klaviyo

  
  

Source: Klaviyo

7. Reduce Mailbox Unavailability Issues

• Use sunsetting and segmentation flows to suppress profiles with unavailable mailboxes or consistent bounce histories.

• Temporarily suppress these profiles until further investigation determines whether they should be removed permanently. Klaviyo

8. Prevent Invalid Sender Address Issues

• Double-check that your default sender email address is properly spelt and exists as a functioning email address.

• Ensure your email is compliant with industry standards to avoid being flagged or rejected by mailbox providers. Klaviyo

  
  

Source: Klaviyo

9. Handle Ambiguous or Unclassified Bounces

• When you receive "Unclassified" bounces, suppress these profiles temporarily until a clear resolution is available.

• If these are soft bounces, it may indicate temporary issues with the recipient’s mailbox provider that could be resolved over time. Klaviyo

10. Monitor ISP Trends

• Track bounce patterns by ISP (e.g., Gmail, Outlook, Apple Mail). If bounces are concentrated on one provider, investigate potential issues such as spam filter triggers or technical blocks.

• Adjust your campaigns for those segments by sending plain-text emails or removing problematic content. Klaviyo

Section 5: Tools for Tracking and Managing Bounces

The Best Tools for Managing Email Bounces

Klaviyo 

• Advanced reporting to track bounce metrics.

• Automates segmentation to exclude bounced addresses. Klaviyo 

  
  

Source: Klaviyo

Mailchimp

• Simple and user-friendly bounce tracking. For comparative insights, see Klaviyo vs Mailchimp.

• Offers insights into why emails bounced. Mailchimp

  
  

Source: EmailListValidation

NeverBounce

• Validates email lists and removes invalid addresses.

• Reduces hard bounces effectively. NeverBounce

  
  

Source: OnlyInfluencers

Litmus

• Tests emails across platforms to identify potential deliverability issues.

• Highlights content errors or formatting problems that could cause bounces. Litmus

  
  

Source: Litmus

Section 6: Long-Term Strategies for Bounce Management

1. Analyse Metrics Regularly

• Regularly monitor bounce rates, open rates, and click-through rates to identify trends and take corrective actions.

• Establish bounce benchmarks by industry to track your performance effectively. For example, industries like retail often tolerate bounce rates under 2%, while B2B can see slightly higher rates. Klaviyo

• Use analytics tools like Klaviyo to track email performance and segment audiences based on bounce behaviour.

2. Implement A/B Testing for Continuous Improvement

Run A/B tests to identify what reduces bounces and increases engagement. Focus on elements like:

• Subject Lines: Test urgency, personalisation, and emojis to see what resonates.

Source: Elastic Email

• Email Timing: Send at different times to find the optimal delivery window for your audience.

• Sender Name: A recognisable sender name can reduce the chances of your email being flagged as spam.

  
  

Source: Zapier

3. Link Bounce Management to Deliverability Goals

• Reduced bounce rates directly impact email deliverability and sender reputation. Treat bounce management as an integral part of your deliverability strategy.

• Aim for a holistic approach by improving email content, maintaining clean lists, and engaging with high-value subscribers.

4. Repair Deliverability in time for seasonal sales

• Seasonal sales and holiday campaigns bring higher email volumes, which can strain deliverability if not managed properly. Plan by implementing list cleaning, infrastructure warm-up, and monitoring bounce rates to ensure your emails reach inboxes during these critical periods.

• Use a yearly email calendar to map out high-volume periods like Black Friday or Valentine’s Day. Maximise these campaigns with insights from Mastering BFCM: The Ultimate Guide (2024).

Conclusion

Email bounces may seem like a minor issue, but they can quickly undermine your campaigns by damaging your sender's reputation and reducing engagement. High bounce rates mean fewer opportunities to connect with your audience and achieve your marketing goals.

By understanding the differences between hard and soft bounces, cleaning your email list, and implementing strategies like double opt-in and ISP monitoring, you can significantly reduce bounces and improve deliverability. These steps not only keep your emails out of spam folders but also enhance trust and ROI.

Key Takeaways

• Know Your Bounces: Hard bounces are permanent, but soft bounces can be fixed.

• Protect Your Reputation: High bounce rates can hurt your sender's reputation and push emails to spam.

• Clean Your List: Use tools like NeverBounce to remove invalid emails and keep your list healthy.

• Use Double Opt-In: Confirm emails during sign-up to avoid fake or wrong addresses.

• Watch for Patterns: Check bounce trends by email providers to spot and fix issues.

• Simplify Emails: Keep emails short, under 110KB, and avoid large attachments.

• Use Helpful Tools: Platforms like Klaviyo can track and manage bounces automatically.

Struggling with email bounces?

Let us help you discover tailored solutions to tackle hard and soft bounces effectively. Click here for a free audit and optimise your email strategy today.