You will get an email saying Barracuda has a “HighAlertInQueue”. This means someone sent a mass email or something got bogged down.
Login to Barracuda and on the main status page towards the top right, there will be a label called “In/Out Queue Size” with a number (ex: 0/17). This should be red which generates the alert. Just monitor it for a minute and see if the number is going down.
If the number still does not go down, reboot the Barracuda device. Go to Basic => Administration => Restart (at the bottom)
If it is STILL slow, login to “YourMailServer” and restart the services associated with your email server application. Reboot the mail server if you still have issues.