When upgrading from a build older then 3.5.12.012 to a build 0.12 or above, you should pay attention to the Outbound SMTP host/Smart host configuration. This picture below shows the configuration option.
The release notes tell the following:
Fix: Now honors outbound BASIC > Administration > ‘SMTP host/Smarthost’ for mail delivery when relaying (recipient domain is not on the box). Before this, the system would only deliver quarantine messages and bounce messages to the smarthost. 
When upgrading to firmware version 3.5.12.012 or higher a number of customers have been caught out by a change in the operation of the SMARTHOST setting. This option was used just to route notifications and reports from the Barracuda. On the new firmware, if you have anything entered in the smart host field ALL outbound mail will be forwarded via it.
Multiple customers entered the internal mail server in the field to deliver the notifications and reports. After upgrading the customers weren’t able to send mail. Of course the reason is simple, all outbound mail is trapped in a loop.
The internal mail server sends the mail to the Barracuda and the Barracuda, like the smart host specifies, sends the mail back to the internal mail server. You have to clear the smart host field, unless you implicitly need to use it.
A customer updated the firmware from a Barracuda SPAM &Virus 300 firewall. The firmware was upgraded from version 3.4 to version 3.5.12.024. After the upgrade no email was coming in or going out through the Barracuda firewall.
All email was blocked and the following reason was visible in the message log:
Mail Protocol Violation
At first I couldn’t find a reason why all mail was blocked, so I contacted Barracuda and established a remote connection with Barracuda for remote troubleshooting. (I really like that feature). Finally the engineer found the problem. The Maximum Message Size value under Advanced – Email Protocol – SMTP Configuration was set to:
Yep, you read that correctly. I have no idea where that value came from. So I changed it back to the recommended value of 100 MB. After changing the value, mail started coming in and going out again through the Barracuda.
While troubleshooting a Barracuda Spam Firewall 300 I found a forum on internet, which shows you how to get an extra tab under the Advanced configuration of the Barracuda Spam Firewall. The “secret” configuration page is enabled with the following steps:
You will now get the extra tab Expert Variables like shown below.
I have a customer running a Barracuda SPAM firewall 300. The customer has the specific request that only the administrator can look at Quarantine messages and users shouldn’t get their own Quarantine inbox. To accomplish this I have configured the Quarantine Type: Global.
I see that all Quarantine messages are delivered in the globally configured mailbox. But sometimes the Barracadu still automatically creates an Account Address under the Users tab. The user from that Account has than the ability to look at their own quarantine messages. I thought it would help to configure the option New User Quarantine State to No, but this has no affect.
Does somebody know who to disable the function to automatically create User Accounts on the Barracuda SPAM firewall 300…??