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In what specific situations will my Email Security Gateway send an NDR (bounce) message to the sender?

  • Type: Knowledgebase
  • Date changed: 10 months ago

Solution #00004175


This solution applies to all Email Security Gateways.


In the Email Security Gateway, NDR messages for blocked spam messages are enabled under Advanced > Bounce NDR Configuration.

On firmware 4.1 and below: Basic > Spam Scoring > Spam Bounce (NDR) Configuration. The Barracuda will send a bounce message when NDR on Block, NDR on quarantine, or notify on content based interception are configured to Yes. Note: Sending bounce messages is not recommended due to backscatter concerns. For more information on backscatter, please see Solution #00001720.

NDR (bounce) messages are sent by the server which last had the entire message. Since the Barracuda does not receive the entire message when blocking a message at the connection level it will not send a bounce message. This includes blocked domains and email addresses, invalid recipients, blocked recipients, SPF, blocked IP addresses, RBLs, Barracuda Reputation, reverse DNS, and rate control.

The Barracuda will send an NDR for all other blocks (i.e. intent analysis, spam scoring, fingerprint, header\body\subject policies, character set policies, viruses, and attachments).

Blocked virus notifications are configured under:
Basic > Virus Checking > Virus Notification

On 3.5 Firmware and below, blocked attachment notifications are configured under:
Block/Accept > Attachment Filtering > Block Notification.

On 4.0 Firmware and above, blocked attachment notifications are configured under:
Advanced > Bounce/NDR settings > Attachment Block Notification.

Additional notes:

Because many organizations have learned about backscatter issues, most no longer send traditional bounce messages. The Barracuda will issue an SMTP error code if it blocks a message and then relay this code to the sender's email server. That email server decides if it will notify the sender that the message did not go through.

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