Thanks for bringing this to our attention. I have added it to our internal tracking list for further investigation.

We are looking at making it possible to manage rules across protocols. As we do so, we intend to support persistence of client side rules first, and then later add the capability to manage server side rules.

The BETA build that was released on Friday (build 7391) includes a fix for handling the EWS rules request from eM Client. This fix only eliminates the error in eM Client and does not yet provide any support for rules handling.