Barracuda Email Security Gateway
Why am I seeing a decrease in the number of emails processed by the Barracuda Spam & Virus Firewall?
Scope:
Email Security Gateway firmware release 3.5.12.010 and higher.
Answer:
The reason you are seeing a decrease in the number of emails being processed by the Email Security Gateway firmware release 3.5.12.010 and higher is because rate control violations are now returning a 421 SMTP error to the client. A 421 SMTP error means the service is not available and the connection will be closed. In previous firmware versions, the Email Security Gateway would return a '5xx' error after reaching twice the threshold set for rate control.
Link:
http://www.barracuda.com/kb?id=50160000000He2e