Spam Bounce Non-Delivery Reports (NDRs)
The Barracuda Email Security Gateway sends NDRs to email recipients and senders when one of their messages is blocked. The NDR contains a brief explanation of why the Barracuda Email Security Gateway blocked the message. Information that you may want to add to an NDR includes the contact information of the Barracuda Email Security Gateway administrator so that internal users know who to contact if they have questions about a blocked message.
The ADVANCED > Bounce/NDR Messages page in the Barracuda Email Security Gateway web interface allows for customizing the information in an NDR and for selecting the default language to use in the message.
By default, your Barracuda Email Security Gateway is configured to NOT send an NDR to a sender when the Barracuda Email Security Gateway blocks their email (see the NDR on Block setting on the ADVANCED > Bounce/NDR Settings page). You may want to enable NDRs to alert legitimate senders that their message has not been delivered to the recipient. However, if the email came from an illegitimate source such as a spammer, then sending a bounce notification is not necessary.
Additionally, many spammers spoof valid domains, and you don’t want to send bounce messages to your domain if it is being spoofed. Sending bounce messages to illegitimate senders, or to senders who were spoofed and did not actually send the offending message, is known as “backscatter”. Backscatter can increase the load on your Barracuda Email Security Gateway and may generate a lot of email to fake addresses or to senders whose email addresses were spoofed by a spammer. Your domain could also end up on a real-time blocklist as a consequence.
If your Barracuda Email Security Gateway rarely blocks a legitimate email, consider setting NDR on Block to No for Inbound and/or Outbound mail to reduce backscatter.