Have you set your indexing options in windows to also index the new mounted Drive?
To do this in win 7
Control Panel -> Indexing Options -> Modify -> Add on Relevant Locations.
I'm guessing in windows, windows Index prefers to have it in the default location of 'outlook files' in my documents (You'll notice you cannot change the path on this in the indexing options), I'm guessing if you add the boxcryptor path on it may (or may not) pick it up, so it may not be a work around for you, but its worth a try
The other option would be to have your outlook file where it is, and use a program to sync outlook file over to your encrypted path where needed - such as goodsync, etc.
hope it helps