The Barracuda Email Security Service rate control feature protects your organization 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 for inbound mail is configured on the Inbound Settings > Rate Control page. Rate control for outbound mail is configured automatically by the Barracuda Email Security Service. See Outbound Rate Control for more information.
The rate control mechanism counts the number of messages for a domain from a sender (a single IP address) over a half-hour timeframe and compares that number to the Maximum Messages per Sender IP Address/ 30 minutes threshold you set on the page. If the number of inbound messages for a domain from a sender (a single IP address) exceeds this threshold within a half hour period, the Barracuda Email Security Service defers any further connection attempts from that particular IP address until the next half hour time frame and logs each attempt as Deferred in the Message Log with a Reason of Rate Control.
Inbound Rate Control Exemptions
You can exempt trusted IP addresses from inbound rate control by adding a trusted IP address to the Rate Control Exemption list on the Inbound Settings > Rate Control page. Organizations that relay email through known servers or communicate frequently with known partners can and should add the IP addresses of those trusted relays and good mail servers to this list. Senders and IP addresses cannot be exempted from outbound rate control.