All Barracuda Spam Firewalls, firmware versions 3.5.10.027 and above.
The Trusted Forwarder feature (on the Basic > IP Configuration page) is the answer. Adding the IPs of mail proxy servers into this field (both internal and external are valid) will cause the Barracuda to look at the headers of each email coming from those relay IPs to determine the true source IPs of those emails and use the source IPs when performing the SPF, Rate Control, RBL, and Barracuda IP Reputation checks.
Having a proper trusted relay set up will allow the Barracuda to more easily identify emails that should be blocked by the Barracuda Reputation Service, RBLs, or the Rate Control feature. It will also help SPF by ensuring the sending IP used when checking for SPF is the proper one. In general, any IP that is listed in the old SPF Trusted Forwarder list (on the Advanced > Email Protocol page) should be entered into the Trusted Forwarder list on the Basic > IP Configuration page.
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