Troubleshooting error code 6034 – SUPPRESSED BOUNCE

The case

If your outbound email traffic is failing with error code 6034 – EC_SUPPRESSED_BOUNCE, it means that the recipient’s email address has been added to a suppression list, preventing successful delivery. This typically occurs when a recipient’s mailbox provider responds in a manner that results in the address being suppressed from future email deliveries.

In other words, a previous email sent to the recipient was either undeliverable or marked as spam. As a result, their address was automatically added to an internal suppression list, preventing future emails from being sent to them.


Suppression list
A suppression list is a database of email addresses that should not receive certain messages. These lists are an essential tool for managing email deliverability and ensuring compliance with email regulations.
 
– What it contains: Suppression lists include email addresses of hard bouncers, spam complainers, and over-quota mailboxes (those that cannot receive more emails due to full inboxes).

– Why it’s important: Suppression lists help maintain a good sender reputation by preventing emails from being sent to invalid or problematic addresses. This reduces bounce rates, avoids complaints, and increases the likelihood that your emails reach engaged and relevant recipients.
 
Reasons for suppression
There are three primary reasons why an email address might end up on a suppression list:

1. Bounce – The email was undeliverable, either permanently or temporarily
An email bounce occurs when an email is not delivered due to rejection by the recipient’s email server.

Bounces can be classified into two categories:
Hard bounce – A permanent delivery failure, such as when an email address is invalid.
Soft bounce – A temporary issue, such as a full inbox or a temporary problem with the recipient’s email service provider.
Soft bounces can often be resolved by resending the email after a period of time. Hard bounces, however, are permanent, and the email address should be removed from your active lists to avoid delivery issues in the future.

2. Complaint – The recipient has marked the email as spam
3. Over-quota – The recipient’s inbox is full and cannot accept new emails
 
Additional information on suppression lists can be found here.
 
Check the status of your email traffic
To troubleshoot and monitor your email traffic, you can verify the status of your messages in your Infobip account using two primary methods:
 
1. Logs
Start by logging into your Infobip account. Navigate to Analyze → Logs. Here, you can apply filters to adjust the date range and message status (for example, Undeliverable).
If needed, you can search by specific email addresses to get detailed insights into delivery issues.

 
2. Reports
Navigate to Analyze → Reports, where you can filter undeliverable and expired messages within the report. This will create a report that will provide a broader overview of any traffic issues related to failed deliveries.
 
Good to know
While reviewing your logs or reports, you may encounter error code 6010 – EC_RECIPIENT_INBOX_FULL. This error occurs when the recipient’s mailbox has reached its storage limit, preventing them from receiving additional emails. To resolve this, it’s essential to contact the recipient and request that they clear their inbox.

How the suppression process works with 6010 error
When an email triggers a 6010 error, indicating a full inbox, the system adds the recipient’s email address to the suppression list. Even if the recipient clears their inbox before the seven-day period ends, emails sent to that address will remain suppressed during the suppression period. As a result, the email will first return error code 6010, followed by 6034, which indicates suppression.

This suppression policy is designed to protect your domain’s sender reputation. Continuously sending emails to addresses with full or invalid inboxes can harm your deliverability and cause your messages to be flagged as spam.
Once the seven-day suppression period is over, emails will resume delivery if the recipient’s inbox has been cleared.

Steps to resolve the issue

Managing suppression lists via API
In case your domain is utilizing dedicated IPs, you can manage your suppression lists more effectively with the use of Email Suppression API endpoints. These endpoints allow you to automate suppression list management tasks such as uploading and deleting email bounces and spam complaints via API.

Instructions for using the API can be found in the API documentation under the Email Suppression section.

Managing suppression lists via Infobip account
Information on managing your suppression lists directly through your Infobip account can be found under Manage suppressions.
 
Important to note
While it is currently not possible to remove entries from the suppression list due to an over-quota issue (recipient inbox full), you can still retrieve information on whether an email address is listed for this reason.
 
Successful email campaigns rely on good list hygiene and keeping bounce rates low. Suppression lists play a critical role in this by ensuring emails are not sent to invalid addresses, addresses whose inboxes are unable to accept traffic, or recipients who have marked your messages as spam.
Maintaining a clean suppression list helps improve deliverability, maintains a positive sender reputation, and ensures your emails reach the right audience.
 
Contact Support

If you’ve followed the recommendations above but are still encountering issues with removing the suppression, are unsure why email addresses are being suppressed, or are not using dedicated IPs, 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 and sender: The specific domain and sender from which the traffic is being sent.
– Email address: The specific email address that is returning this error code.