All Barracuda Spam Firewalls upgrading from firmware version 3.5.10.015 or below to a version newer than 3.5.10.015.
If you are using hostnames rather than IP addresses to specify your destination mail servers (configured under the Domains tab of the Barracuda Spam Firewall's web interface), upgrading to a version newer than 3.5.10.015 may interrupt mail delivery.
Firmware version 3.5.10.016 introduced DNS caching on the Barracuda Spam Firewall. While this decreases load on your DNS servers, it may use external DNS servers to resolve internal hostnames. To remedy this problem, go to the Basic > IP Configuration page, scroll down to the DNS server configuration area, make sure an internal DNS server is listed, and specify the Use Only These Servers option as Yes. This will ensure the Barracuda Spam Firewall does not look to any other DNS servers to resolve your internal hostnames. All mail messages in the outbound queue should begin to deliver themselves to your mail server immediately after making this change; please allow 15 minutes for all of the messages to be delivered.
If you encounter any further issues, please contact Barracuda Networks Technical Support.
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