X1 Professional Client was free but it now cost $50, and worth every cent (and I am in no way affiliated with that company).

I use Outlook 2007 and have always saved important (to me ) emails, some with very large attachments.  Eventually the *.pst becomes enormous and unmanagable, and takes Outlook forever to open unless they are archived in groups and save as separate pst files which can be stored and backed up.  For example, create a personal folder file called "My emails from 1_2001 to 12_2004.pst"  and another as "My emails from 1_2005 to 12_2007.pst". 

In my case, the average size of the backed up pst files described above is 1 gig to 2.8 gigs.

Using the Outlook/File/Data File Management/Data Files tab, you can point to the default pst file (e.g. a pst file that contains all emails from 2007 to the present) that opens by default with Outlook.  However, at any given time, you can open a previous pst archive, as needed.

Here's the key to the kingdom.  Using the program X1, which is not free but worth every penny, one can maintain an index of all the mail in the old pst files and even MS Exschange files (i.e. *.ost files) and instantly locate and open an old email without having it as the active or default pst file in Outlook.  One can search by name of sender, or receiver, or attachment file type and all manner of wild card combinations.

For anyone that manages or searches humungous piles of emails ranging from the recent past to the very distant past, this is a friggin' awesome system.

Note of caution:  Be sure to backup the original pst file before embarking on the Outlook archiving feature if you are not familiar with it.  I searched the web and found some helpful articles which describe exactly how to do it.  I deleted the links or I would have attached them. 

p.s. I have always been shackled to Outlook, for business reasons only. However, once you learn, it is relativley simple.   Don't overlook the power X1.    I have tried many other software products that pretend to manage Outlook mail, and have not found anything better than groups of pst files indexed by X1.

p.p.s.  This virtually eliminates the need to categorize anything.

p.p.p.s  I use X1 only for Outlook email.  I use Locate32 and dtSearch for most other desktop file searching requirements.

I like the idea of creating a limited user account and creating permissions so that personal files can only be read by me.

However, the ‘Make this folder private’ option is grayed out on the folder properties tab.  My understanding is that you can only set permissions for files and folders on the same drive where Windows is installed, which is C: drive in my case.

Is there any way to set permissions for folders on the D: drive partition?