This solution applies to Barracuda Spam Firewall models 300 and above, all firmware versions.
When the Barracuda Spam Firewall creates an account for a user, it will send a welcome message to that user. If the user does not exist on the destination mail server, that mail server may send a bounceback (NDR) response to the "Reply to" address (if it has been configured to send bounce messages).
To prevent this, any of the following changes can be made:
- Change the Quarantine Reply-To Address on the Basic > Quarantine page. Note that this will affect a user's ability to reply to the Quarantine Summary messages if necessary.
- Turn off the automatic creation of new quarantine accounts by setting the New User Quarantine State option to Off on the Basic > Quarantine page. The quarantine accounts will then need to be created manually by the administrator of the Barracuda.
- Enable the Barracuda Spam Firewall's recipient verification. The Barracuda can then verify recipient email addresses and block mail to invalid recipients without creating quarantine accounts for them.
Recipient verification can be performed using one or more of the following three methods:
- The Barracuda can communicate with an LDAP/Active Directory server to verify recipients. LDAP verification can be configured from the Domains > Domain Manager page. See Solution #00002192 for more information on setting up LDAP/Active Directory recipient verification.
- The Barracuda can establish a connection to the destination mail server over SMTP for each incoming email message to determine if the recipient is valid. If the mail server responds with a 500 level error code, then the email will is rejected. This requires that the mail server provide the correct response to invalid recipients. Please see your mail server's documentation for more information on how to enable recipient verification on your mail server.
- The Valid Recipients feature (also known as native recipient validation) may be used in addition to either of the other two recipient verification methods listed above, or in place of them. It is used by specifying a list of valid email addresses directly on the Barracuda Spam Firewall on the Domains > Edit Domain page. See Solution #00003395 for more information on setting up the Valid Recipients feature.
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