What is an Email Bounceback Message?

An email bounceback message, also known as an Non-Delivery Report (NDR), is a message that is provided to the sender of an email by their own mail server or email service provider (a 3rd party that sends mail on behalf of a domain) whenever an email bounce occurs. This message contains details about why a single email bounced, including the error code and error description provided by the intended recipient's mail server.

The reasons why messages bounce vary and range from unresponsive servers, nonexistent email addresses, and full inboxes. There are several types of email bouncebacks, but the two main categories are hard bounces and soft bounces.

A hard bounceback happens when one of your emails becomes permanently undeliverable to a specific address. It indicates a permanent reason an email cannot be delivered, such as the recipient email address/domain does not exist or the recipient email server blocked delivery.

Hard bounces cannot be fixed. If you receive a hard bounceback from your outbound mailing list, simply remove the email address. Having repeated hard bounces might result in your emails being blocklisted, which is never ideal.

A soft bounce occurs when a server has temporarily rejected your email. It is typically a minor issue and can be resolved by resending your message later. Reasons for soft bouncebacks include the recipient's mailbox is full, a server is down, and the size of the sent email is too large.

Whether bounces occur from a marketing campaign or general business email, be sure to identify any error messages in your inbox and take action before they damage your sender reputation and deliverability.

Email Bounceback Analyzer Tool

MxToolbox has a free Email Bounceback Analyzer Tool that diagnoses the reasons your email is being bounced. It utilizes our unique centralized repository of bounceback messages that span hundreds of email provider responses.

When you get a bounceback error email from an inbox provider, simply copy the full message (including the header) and paste it in the text box. Next, click the “Analyze Message” button. Results will then be displayed to help you achieve inbox delivery.

If we do not have the bounceback response specific to you in our library, the Bounceback Analyzer will notify us. We will then find the needed reply and send the results directly to you.

We also offer a consolidated database of bounceback error messages assorted by mailbox provider here. This page provides more insight and specific content into why your outgoing emails are bouncing instead of being delivered to recipients’ inboxes.