I have asked Cisco this question since early 2010 and got the following answer:
we are working directly with Microsoft on this and should have a release soon that supports it vs. Riverbed that "cheat" by doing some reverse engineering of the MAPI encryption...
I also asked about SMB signing in CIFS file shares.Basically if you use SMB signing, you do not have CIFA AO acceleration. This means that the traffic is treated as Generic TCP traffic and is not accelerated specifically with the CIFS accelerator (and the cache used is not the CIFS cache but the DRE shared cache)... Still - as far as I know - no release that fixes that either
Patrick