As part of a mail migration project from one Exchange organization to another, we need to be able to prevent users from moving/copying messages between their accounts in each organization. (Yes, users will think this is evil; no, it's not my decision; yes, users will hate us.)
Luckily, we thought, Outlook 2010 provides the DisableCrossAccountCopy registry value/policy (cf. http://technet.microsoft.com/en-us/library/ff800883.aspx). (Because you can't do multiple Exchange organizations in a single profile before Outlook 2010, this only matters on Outlook 2010. Yes, I'm ignoring for the sake of this question copy/move to/from the filesystem.)
In our test lab, in a test forest with a test Exchange organization, with a second Exchange account added to the profile in either of the "real" Exchange organizations, with the value set to "*", everything works as expected.
On a workstation in one of the production domains, however, the setting does not seem to work. We have tried it under HKCU, HKLM, HKCU\Software\Policies, and HKLM\Software\Policies. It simply seems to be ignored.
The value was set in the OCT on a test machine, but the OCT (and the ADM/ADMX file) have the wrong type for the value. We have located the value in the registry and removed it everywhere it is found, we think, and put it back in HKCU, but it still isn't taking. At the moment, a clean Outlook install is not an option - even if it was, we at this point would need to know what to do to fix the pushed copy (I didn't push the copy out to thousands of machines, I've just been asked to help clean up the current mess).