To follow on from the blog entry about DisablePST, another (very) common Outlook registry key which is used is :
The registry key stops users from ‘growing’ PST files. This happens pretty much whenever a PST file is accessed, so adding this registry key effectively stops PST usage. This is slightly different to DisablePST. The difference is that with PSTDisableGrow this stops ALL access to PSTs.
The Enterprise Vault Outlook Add-in uses PSTs to temporarily store downloaded items, as well as for Vault Cache, and Virtual Vault. Disable PST ‘growth’ has a disastrous effect.
Fortunately PSTDisableGrow has a partner registry key called PSTDisableGrowAllowAuthenticodeOverrides
This registry key lets developers to programmatically still use PSTs just as before.
So both of these have to be set. Failure to do so will lead to problems, as described in the numerous technotes, articles and forum posts.