How can I test bounce alerts and what are some example bounce email addresses?
Michael Ko
Co-founder & CEO, Suped
Published 12 Jul 2025
Updated 15 Aug 2025
6 min read
Understanding how your email system handles bounced emails is essential for maintaining good sender reputation and effective communication. If you're setting up bounce alerts to notify your sales team or customer support about invalid email addresses, you'll want to test this system thoroughly.
Testing bounce alerts ensures that your internal processes for managing undeliverable emails work as expected. It helps confirm that the right people are notified promptly when an email cannot be delivered, allowing for timely data cleanup and follow-up. A well-configured bounce management system can significantly improve your email deliverability over time.
Understanding bounce alerts
The most straightforward way to test a bounce alert is by sending an email to an address that you know does not exist within your own domain. This approach reliably generates a hard bounce, triggering your configured alerts. For example, you could try sending to something like nonexistentuser@yourdomain.com. Your mail server should immediately recognize that this address is not valid for your domain and issue a bounce notification.
Some email service providers and testing services offer specific email addresses designed to generate various types of bounces. These can be incredibly useful for simulating different scenarios, such as full inboxes or temporary server issues. Using these test addresses allows you to verify that your bounce handling logic is robust and can correctly classify different bounce types, like a soft bounce versus a hard bounce.
When generating intentional bounces, it is important to do so sparingly and avoid high volumes. Sending many emails to non-existent addresses can negatively impact your sender reputation, making you appear as a spammer. Focus on targeted tests to confirm functionality rather than large-scale simulations.
Practical methods for testing bounces
To effectively test bounce alerts, you can use specialized addresses that are configured to return specific bounce types. For instance, some services provide addresses that will explicitly hard bounce, indicating an invalid recipient. Other addresses might soft bounce, simulating a temporary delivery issue like a full mailbox.
For hard bounce testing, addresses such as reject@wordtothewise.com are known to return a permanent rejection. For soft bounce testing, you might use defer@wordtothewise.com, which simulates a temporary deferral. These types of addresses are valuable because they provide predictable bounce behaviors.
When testing for a no such user hard bounce from a major provider like Gmail, you should expect a specific error message. For example, sending to a non-existent Gmail address will typically return a 550 5.1.1 response. This type of error is definitive proof that the recipient address does not exist.
Example Gmail 'No Such User' Bounce Message
550 5.1.1 The email account that you tried to reach does not exist. Please try double-checking the recipient’s email address for typos or unnecessary spaces. Learn more at https://support.google.com/mail/?p=NoSuchUser g19si3566922ejh.138 - gsmtp
Be aware that if you send to an invalid domain, such as a typo like example@gmail.co, the bounce may originate from your own sending server (MTA) if it determines the domain lacks a valid mail server, resulting in an "internal recipient blackholed" message. This indicates your MTA didn't even attempt to deliver the email, which is different from a bounce generated by the recipient's server.
Distinguishing hard and soft bounces
Email bounces are broadly categorized into two types: hard bounces and soft bounces. Hard bounces indicate a permanent delivery failure, meaning the email address is permanently invalid or non-existent. Soft bounces, on the other hand, signify a temporary issue, such as a full inbox, server downtime, or the recipient's email server being temporarily unavailable. Understanding the difference is crucial for effective email bounce management.
Hard bounces require immediate action. Continuing to send emails to hard-bounced addresses signals to internet service providers (ISPs) that your list quality is poor, which can lead to your emails being marked as spam or your sending IP address being added to a blocklist (or blacklist). Soft bounces are often temporary, and most email systems will retry sending the email a few times before classifying it as a persistent issue. Monitoring soft bounces can help you identify trends or systemic problems with a recipient's server.
It is important to have a robust system to troubleshoot email bounce messages. Regular clean-up of your email lists by removing hard-bounced addresses is a fundamental best practice for maintaining high deliverability rates. For soft bounces, investigate common causes like full inboxes or temporary server issues before deciding to remove the address.
Hard bounces
Permanent failure: Indicates the email address does not exist or is invalid.
Examples: "unknown user," "host unknown," or "mailbox disabled."
Action required: Immediately remove these addresses from your mailing list to protect your sender reputation.
Soft bounces
Temporary issue: Indicates a transient problem preventing delivery.
Examples: "mailbox full," "server unavailable," or "message too large."
Action required: Monitor and retry. If a soft bounce persists, consider removing the address.
Impact on deliverability and mitigation
High bounce rates, especially hard bounces, can significantly harm your sender reputation. ISPs use bounce rates as a key indicator of list hygiene and sending practices. A clean list with low bounce rates signals that you are a legitimate sender, increasing the likelihood that your emails reach the inbox. Conversely, a high bounce rate can lead to your emails being routed to the spam folder or even outright rejected.
To minimize bounces and maintain a healthy sender reputation, proactive email list management is crucial. Regularly validate your email addresses and segment your lists based on engagement. Disengaged subscribers or old email addresses are more prone to bouncing or becoming spam traps, which are extremely detrimental to deliverability.
Implementing email authentication protocols like DMARC, SPF, and DKIM also plays a vital role. These protocols verify the legitimacy of your emails and help prevent spoofing, which in turn can reduce complaint rates and improve overall deliverability. Ensuring that your sending infrastructure is properly configured for these standards is a fundamental step in preventing bounces related to authentication failures. You can use our email deliverability tester to check if your infrastructure is set up correctly.
Best practices for bounce prevention
Email validation: Use a validation service to clean lists before sending campaigns.
List hygiene: Regularly remove hard-bounced addresses and manage soft bounces.
Authentication: Ensure SPF, DKIM, and DMARC are correctly configured.
Monitor reports: Utilize bounce and complaint notifications, such as from Amazon SES.
Views from the trenches
Best practices
Use dedicated testing email addresses that are known to generate specific bounce types, like hard or soft bounces.
Verify that your bounce alert system correctly classifies different bounce types to ensure appropriate follow-up actions.
Integrate bounce data into your CRM or sales tools to automatically update contact records and prevent future sends to invalid addresses.
Regularly monitor your bounce rates and analyze bounce messages to identify common issues or emerging trends in your sending.
Common pitfalls
Attempting to test bounce alerts at a large scale, which can negatively impact your sender reputation and lead to blocklisting.
Using randomly generated email addresses without a valid mail server, which may trigger an internal rejection rather than a true bounce from a recipient's server.
Not removing hard-bounced email addresses from your mailing lists, leading to continued sending to invalid recipients and reputation damage.
Ignoring soft bounces, as persistent soft bounces can indicate underlying issues that might eventually lead to hard bounces or reputation problems.
Expert tips
Focus on testing the integration between your email sending platform and your bounce alert system to ensure seamless data flow.
Understand the nuances of different bounce codes to accurately diagnose delivery issues and implement targeted solutions.
Implement a feedback loop from your bounce alerts to your email list management process for automated suppression.
Consider setting up DMARC reporting to gain deeper insights into bounce patterns and potential abuse of your domain.
Expert view
Expert from Email Geeks says the best way to test bounce alerts is by creating a non-existent email address on your own domain and sending mail there to generate the bounce. Testing at scale, however, is not a viable option.
November 6, 2020 - Email Geeks
Marketer view
Marketer from Email Geeks says one intentional bounce is acceptable, but sending at any volume or frequency risks making you appear as a rogue sender.
November 6, 2020 - Email Geeks
Staying on top of your bounce data
Testing bounce alerts and understanding bounce types are crucial steps in maintaining a robust email marketing or transactional email system. By using intentional bounce addresses and carefully observing the responses, you can ensure that your bounce management processes are effective. This proactive approach helps preserve your sender reputation and improves your overall email deliverability.
Use a validation service to clean lists before sending campaigns.
Utilize bounce and complaint notifications, such as from Amazon SES.
