We have promoted SPF checking on inbound mail forwarding from beta to normal production. All members can now optionally enable SPF checking on inbound mail destined for their domains via the “email” settings in their domain options.
If the SPF validation equates to hardfail for a domain with SPF validation enabled, our mail servers will reject the inbound message, all other outcomes will be prepended into an additional SPF-Received: header in the message and processed normally. Members can then add additional filters keying on this header in their mail clients or downstream MTAs.
For more details on SPF and how it works, please see easySPF.com