Are you struggling with email bounce backs? Do you want to improve your email deliverability and ensure that your messages reach their intended recipients? In this comprehensive guide, we will delve into the world of email bounce backs, exploring the different types of bounces, their causes, impacts, prevention strategies, and management techniques. By understanding the intricacies of email bounce backs, you can optimize your email marketing campaigns, enhance your sender reputation, and achieve better results.

What are Email Bounce Backs?

Email bounce backs, also known as email bounces or bounced emails, refer to the failed delivery of email messages to recipients. Instead of reaching the intended inbox, these emails "bounce" back to the sender, resulting in non-delivery. Bounce backs are essentially error messages generated by the recipient's mail server or the email service provider (ESP) handling the message.

Email bounce backs are categorized into two main types: hard bounces and soft bounces.

Hard Bounces

A hard bounce occurs when an email is permanently rejected and cannot be delivered. The reasons for hard bounces include:

Invalid or non-existent email address: If the email address you're trying to send to doesn't exist or is invalid, the email will bounce back as a hard bounce.

Domain name doesn't exist: If the recipient's domain name doesn't exist or has expired, your email will be rejected as a hard bounce.

Recipient's mail server blocks the email: In some cases, the recipient's mail server may have strict spam filters or other security measures that result in a hard bounce.

Hard bounces are considered permanent failures, indicating that the email cannot be delivered. It is crucial to remove email addresses that result in hard bounces from your mailing list to maintain list hygiene and improve your email deliverability.

Soft Bounces

A soft bounce is a temporary failure to deliver an email. The reasons for soft bounces include:

Recipient's mailbox is full: If the recipient's mailbox is full, your email may bounce back as a soft bounce. The email service provider will attempt to deliver the email again later.

Temporary mail server issues: If the recipient's mail server is experiencing temporary technical issues or is undergoing maintenance, your email may be temporarily bounced back.

Message size exceeds the limit: Some mail servers have restrictions on the size of incoming messages. If your email exceeds the specified limit, it may result in a soft bounce.

Soft bounces are generally considered temporary and do not require immediate action. However, if a soft bounce persists over multiple delivery attempts, it may turn into a hard bounce. It is important to monitor soft bounces and take appropriate actions to prevent them from becoming permanent delivery failures.

Types of Email Bounce Backs

Email bounce backs can be further categorized into different types based on the error codes provided in the bounce messages. Understanding these types can help you identify the specific issues causing the bounces and take appropriate actions. Here are some common types of email bounce backs:

1. Mailbox Unavailable

This type of bounce occurs when the recipient's mailbox is unavailable. It could be due to reasons such as the mailbox being full, the recipient's account being inactive, or the mailbox being temporarily suspended.

2. User Unknown

A "user unknown" bounce indicates that the email address does not exist or is invalid. This could be because the recipient has changed their email address, the address was mistyped, or the domain name is incorrect.

3. Blocked by the Recipient's Server

If the recipient's mail server blocks incoming emails from your domain or IP address, your messages will bounce back with this type of bounce. It could be due to strict spam filters, blacklisting, or other security measures.

4. Message Size Exceeded

If your email message exceeds the size limit set by the recipient's mail server, it will bounce back with a "message size exceeded" error. This can happen when sending large attachments or including excessive images or multimedia content.

5. Invalid Domain

If the recipient's domain name is invalid, expired, or does not exist, your email will bounce back with an "invalid domain" error. This could be due to a typo in the domain name or the domain no longer being active.

These are just a few examples of the types of email bounce backs you may encounter. Each type provides valuable information about the reason for the bounce, enabling you to take appropriate actions to resolve the issue and improve your email deliverability.

Causes of Email Bounce Backs

Email bounce backs can be caused by various factors. Understanding the underlying causes can help you prevent or minimize the occurrence of bounce backs. Here are some common causes:

1. Invalid or Non-existent Email Addresses

Sending emails to invalid or non-existent email addresses will result in hard bounces. These addresses may have been mistyped, discontinued, or no longer in use. It is crucial to ensure the accuracy of your email addresses before sending out campaigns.

2. Outdated or Invalid Domains

If the recipient's domain name is invalid, expired, or no longer active, your emails will bounce back as hard bounces. Keep track of the validity and expiration dates of the domains on your mailing list.

3. Recipient Mailbox Issues

Issues with the recipient's mailbox, such as a full inbox, can cause soft bounces. These issues are usually temporary, and the email service provider will attempt to deliver the email again later.

4. Mail Server Restrictions

Some mail servers have restrictions on the size of incoming messages or attachments. If your email exceeds these limits, it may result in bounce backs.

5. Spam Filters and Blacklisting

Strict spam filters or being blacklisted by recipient servers can cause your emails to bounce back. It is important to follow email best practices and maintain a positive sender reputation to avoid being flagged as spam.

These are just a few examples of the causes of email bounce backs. Identifying the specific causes for your bounce backs can help you implement targeted strategies to prevent them and improve your email delivery rates.

Impacts of Email Bounce Backs

Email bounce backs can have several negative impacts on your email marketing efforts:

1. Reduced Deliverability

High bounce rates can harm your sender reputation and affect your email deliverability. Internet service providers (ISPs) may flag your emails as spam or bulk mail if they observe a significant number of bounce backs.

2. Wasted Resources

Sending emails to invalid or non-existent addresses wastes your resources, including time, effort, and money spent on creating and sending those emails. By reducing bounce backs, you can optimize your resources and improve your ROI.

3. Damage to Sender Reputation

Consistently high bounce rates can damage your sender reputation, making it harder to achieve inbox placement in the future. ISPs and email service providers monitor sender reputation as a measure of email quality and sender trustworthiness.

4. Missed Opportunities

If your emails consistently bounce back, you may miss out on important communication opportunities with your audience. Whether it's a promotional offer, a critical update, or important information, bounce backs prevent your messages from reaching the intended recipients.

Understanding the impacts of email bounce backs emphasizes the importance of taking proactive measures to minimize their occurrence and maximize your email deliverability.

Preventing Email Bounce Backs

While some bounce backs may be unavoidable, there are several steps you can take to prevent or minimize them:

1. Use Double Opt-in

Implementing a double opt-in process ensures that subscribers provide a valid email address and confirm their subscription. This helps reduce the chances of invalid or mistyped email addresses entering your mailing list.

2. Regularly Cleanse Your Mailing List

Periodically review and cleanse your mailing list by removing invalid or inactive email addresses. This can be done by using an email verification service or monitoring bounce reports to identify addresses that consistently bounce back.

3. Verify Email Addresses at the Point of Entry

Validate email addresses in real-time at the point of entry, such as during the sign-up or checkout process. This can prevent incorrect or invalid email addresses from entering your system.

4. Monitor Bounce Rates

Regularly monitor your bounce rates and analyze bounce reports provided by your email service provider. This will help you identify trends, address underlying issues, and take corrective actions promptly.

5. Follow Email Best Practices

Adhere to email best practices, such as using a reputable ESP, optimizing email content for deliverability, and complying with anti-spam regulations. This will help maintain a positive sender reputation and minimize the chances of your emails being flagged as spam.

6. Segment Your Mailing List

Segmenting your mailing list allows you to send targeted and relevant content to specific groups of subscribers. This helps improve engagement, reduces the risk of spam complaints, and lowers bounce rates.

Managing Email Bounce Backs

When bounce backs do occur, it is essential to manage them effectively:

1. Analyze Bounce Reports

Review bounce reports provided by your ESP to understand the specific bounce codes and error messages. This will help you identify the root causes and take appropriate actions to resolve them.

2. Remove Hard Bounces from Your List

Immediately remove email addresses that result in hard bounces from your mailing list. Continuing to send emails to these addresses will harm your sender reputation and deliverability.

3. Retry Soft Bounces

For soft bounces, your email service provider will typically attempt to deliver the message multiple times. Monitor soft bounces, and if they persist over several delivery attempts, consider removing them from your list or reaching out to the recipient to resolve any issues.

4. Update Contact Information

If you receive bounce backs due to invalid or outdated contact information, reach out to the recipient and request updated details. Keeping your contact information up-to-date ensures successful communication.

5. Seek Professional Assistance

If you're experiencing persistent bounce backs or facing challenges in managing your email deliverability, consider consulting with email deliverability experts or professionals who can provide guidance and support.


Email bounce backs can be frustrating and detrimental to your email marketing efforts. However, by understanding the different types of bounce backs, their causes, and the necessary preventive and management measures, you can optimize your email deliverability and improve your overall email marketing performance.

Remember to regularly monitor your bounce rates, cleanse your mailing list, follow email best practices, and proactively address any issues that arise. By taking these proactive steps, you can ensure that your emails reach the intended recipients, drive engagement, and achieve the desired results from your email marketing campaigns.