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Navigating email bounces: Understanding and acting on failed deliveries

When you communicate via email, it can sometimes happen that a sent message does not arrive at the recipient. This phenomenon is known as a 'bounce'. A bounce can occur for various reasons, ranging from issues with the recipient's email address to server problems. It's important to understand how bounces work and how to respond when they occur.

Notification of Bounces

When an email you have sent bounces, you will receive an email from us. This email will inform you that the email has not been successfully delivered. It contains details about the reason for the bounce, which are crucial for diagnosing the problem and taking appropriate action.

Below is a list of the most common error codes you may encounter in the bounce message, along with an explanation of what they mean.

List of Error Codes and Explanations

554 5.7.1 [internal] recipient address was suppressed due to customer policy

The message was denied because the recipient's address was blocked due to a recipient's policy, such as a request not to receive emails from the sender.

554 5.4.4 [internal] Domain Lookup Failed

The email server was unable to find the recipient's domain name, possibly due to an error in the domain name or issues with the DNS server.

554 5.4.4 [internal] Domain Does Not Exist

The recipient's domain does not exist, which may indicate a misspelled email address or a dissolved domain.

550 5.4.1 Recipient address rejected: Access denied.

Access to the recipient's email address was denied, possibly due to the receiving email server's policy.

552 5.2.2 ...@... user is over quota

The email was not delivered because the recipient's mailbox is full. The recipient needs to make space to receive new emails.

550 5.5.0 Requested action not taken: mailbox unavailable

The recipient's mailbox is unavailable, due to reasons such as a non-existent email address or a temporary problem.

550-5.1.1 The email account that you tried to reach does not exist.

The email account you attempted to reach does not exist, meaning the specified email address is incorrect or the account has been deleted.


Understanding why an email was not successfully delivered helps you take the right steps to prevent similar issues in the future. This may mean contacting the recipient to inform them about the situation, asking them to check their email settings, or specifically requesting domains such as to be whitelisted.

Updated on: 13/06/2024

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