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Backscatter occurs when spammers, hackers or other users with malicious intent, spoof the email addresses of legitimate email users to send spam, viruses or worms. The receiving email server typically rejects the email and sends an NDR message to the spoofed email address. As a result, the legitimate email user receives a bounce message for emails that they never sent.

Invalid Bounce Suppression tags the sender addresses of all outgoing messages sent from the Barracuda Spam Firewall’s outbound relay, or through the Barracuda Spam Firewall – Outbound appliance. The tags are encoded with built-in expiration periods and encrypted to prevent forgery. When an NDR message is received by the Barracuda Spam Firewall, a valid tag must be present in bounce recipient address (i.e., the original sender address) for the bounce message to be delivered. If the bounce recipient address does not contain a tag or if a tag is invalid, the NDR message is rejected. Usage of the Invalid Bounce Suppression feature is transparent to legitimate senders and recipients.

In addition to Invalid Bounce Suppression, the latest Barracuda Spam Firewall version also includes additional rules governing email policy, including new policy rules for character sets used in emails and attachments, reverse DNS resolutions of sending email servers, and full URLs (including query strings) embedded in emails.

Pricing and Availability:

The latest features, including Invalid Bounce Suppression, are available with Barracuda Spam Firewall firmware release 3.5.12 and above. The Barracuda Spam Firewall is available in eight models with prices starting at £599.