In Apple Mail, it is possible to create rules to file your messages for you as they are received. In order to create a rule to move any messages marked as spam by the Barracuda, simply follow these directions.

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If you do not already have a folder that you'd like to use for filing spam messages into, we'll need to create one.

In the "Mailbox" menu, select "New Mailbox..."

Enter "Spam-Barracuda", which we'll use as our folder name, in the "Name" field and click "OK". You should now see a new folder in your folder list named "Spam-Barracuda".

Now, we want to define the rules for filing spam. From the "Mail" menu, select "Preferences..."

In the Preferences window, select the "Rules" icon and then click "Add Rule".

Enter a name for the rule in the "Description" field. For this example, let's call it "Barracuda Spam Messages".

Next, we want to match the "X-Barracuda-Spam-Status" header. Since this does not exist by default, we need to select "Edit Header List" from the leftmost list box.

In the "Message Headers" window that comes up, click the "+" button.

Enter the text "X-Barracuda-Spam-Status" (without the quotation marks) and click "OK"

Select our new header ("X-Barracuda-Spam-Status").

Select "Begins with" from the next list box.

Enter the text "Yes" (without quotation marks).

Finally, select the "Spam-Barracuda" folder we created earlier and click "OK".

Mail will ask if want to apply the new rules to all open mailboxes. You may safely click "Yes" here, and any messages marked as spam by the Barracuda will be filed for you.

You may now close the Mail preferences window.

If you would like to add additional rules to filter out messages with lower Barracuda Spam scores that you still consider spam, see the instructions here.