Why is my domain blocked?

The case

If you’re experiencing issues where all your outbound emails are failing with error code 6016 EC_SENDER_DOMAIN_BOUNCE_BLOCKED, this indicates that your domain has been temporarily blocked. This block is a safeguard designed to protect your domain and IP reputation, triggered by an increase in email bounce rates.

What causes this error?

Before a block is put in place, your domain will experience an increase in the following error codes:

These errors suggest that your recent email traffic contains a large number of invalid or unavailable addresses. When emails are sent to these addresses, they generate the above mentioned 6006 and 6009 error codes, which in turn increase your overall bounce rate.

A high bounce rate indicates that a significant portion of your emails were rejected by the receiving server and were not delivered to the intended recipients.

When your bounce rate increases beyond acceptable levels, Infobip automatically triggers the 6016 error, resulting in a temporary block of your domain to prevent further reputation damage.

Understanding the block and how to address it

Infobip implements this block to help protect your domain, sender and IP reputation, and to maintain email deliverability. As a precautionary measure, Infobip will send you a notification if your bounce rate exceeds 3% within an hour, day, or month. This serves as an early warning, allowing you time to address the issue before the bounce rate reaches the 5% threshold that triggers a block.

To additionally verify if your domain is currently blocked, you can log in to your Infobip account and navigate to Channels and Numbers → Channels → Email → Marketing and Transactional to access your domains.

If your domain is blocked, you will see a yellow exclamation point next to your domain name. Hovering over this icon will also display this message.

Steps to resolve the issue

If your domain is currently blocked, it will be on a 24-hour cooling-off period. After this period, the block will automatically be lifted, and your bounce cycle counter will reset. This time allows you to address the underlying issues that led to the block.

To prevent future blocks and ensure that your email campaigns continue to run smoothly, we recommend implementing the below-outlined best practices, as they are designed to help you manage and reduce bounce rates effectively:

Focus on active subscribers – Make sure you’re sending emails only to individuals who have actively subscribed to your mailing list. Avoid using email addresses from sources like scraped websites, third-party vendors, or purchased lists. By focusing on engaged subscribers, you enhance the relevance of your emails and reduce the risk of bounces.

Leverage Infobip’s email validation service – Take advantage of our email validation service to filter out invalid or inactive email addresses before sending your campaigns. This service helps keep your list clean and can significantly improve your email deliverability.

Information on Infobip’s validation solution can be found on this link.

Routine maintenance – Regularly review and clean your mailing list to remove inactive or invalid addresses. This practice helps lower bounce rates and ensures that your emails reach legitimate recipients. A well-maintained list is crucial for maintaining a positive sender reputation.

Respect unsubscribe requests – Ensure that once a subscriber opts out, they are not retargeted in future campaigns. Respecting unsubscribe requests helps build trust with your audience and prevents potential issues with deliverability. 

Manage mailing volumes carefully – Be cautious about sudden increases in your mailing volumes. Such spikes can lead to higher bounce rates and potential blocks. Gradual and consistent increases in volume are more manageable and less likely to trigger deliverability issues.

Analyze your email reports – Regularly review your email performance reports to identify any patterns or anomalies that could contribute to higher bounce rates.

To generate a report, log in to your Infobip account, navigate to Analyze → Reports, and create a report tailored to your needs.

Detailed information on generating reports can be found in our guide on this link.

For further understanding of how to manage bounce rates effectively, refer to our deliverability recommendations.

Contact Support

If you have followed the recommendations above and are still unsure why your domain was blocked, please don’t hesitate to contact our Support team for further assistance.

You can reach our Support team via [email protected].


Please provide the following information:

– Domain name: The specific domain that is returning this error code.