I am currently using Outlook 2013. I am an avid user of folders to organize my email and have accumulated a fairly large number of them. Everything was working just fine for a while, but recently I noticed an issue with my folders that would cause Outlook 2013 to temporarily freeze up.
This would occur when I would expand my Inbox to view the sub-folders. Then I would click on a folder to view the email it contained. It was at that point, Outlook 2013 would then freeze up, and it would appear to be rolling up each folder slowly until the Inbox was again collapsed.
Sometimes I would do this three or four times before it would allow me to get to retrieve the email I needed from one of the sub-folders. FRUSTRATING!
Turns out this one strange little trick seems to resolve the issue:
With your mouse, drag the Inbox folder below the Outbox.  Once that’s done, drag it back below the Drafts folder.  That’s it!