Barracuda Rate Control

The Barracuda Spam Firewall Rate Control feature protects the system from spammers or spam-programs (also known as "spam-bots") that send large amounts of email to the server in a small amount of time. Rate Control is configured on the BLOCK/ACCEPT > Rate Control page. 

As part of the Connection Management Layer, the Rate Control mechanism counts the number of connections to the Barracuda Spam Firewall in a half hour period and compares that number to the Rate Control threshold, which is the maximum number of connections allowed from any one IP address in this half-hour time frame. If the number of connections from a single IP address exceeds the Rate Control threshold within the half hour period, the Barracuda Spam Firewall will defer any further connection attempts from that particular IP address until the next half hour time frame and log each attempt as deferred in the Message Log with a Reason of 'Rate Control'. 

In this case, for each message deferred, the sender will receive a 4xx level error message instructing the mail server to retry after a predefined time interval. Well-behaving mail servers act upon the defer message and will try sending the message again later, while email from large volume spammers will not retry sending the email again. 

You can exempt trusted IP addresses from Rate Control by adding a trusted IP address to the BLOCK/ACCEPT > Rate Control > Rate Control Exemption/IP range list. Also, any IP address that you enter as a trusted forwarder on the BASIC > IP Configuration page will be exempted from Rate Control.