I've seen some related posts but none seem to directly address why this happening or how to fix. In my Outlook for Mac 2011, my 'message sources' folder is a whopping 65 gig. It's killing my MAC Air. My email inbox only has 30 messages in it. I have dragged emails to an offline folder but, even then, the file wouldn't be more than a gigabyte.

So, can anyone please advise how to reduce this folder size?

Many thanks

2011 1.7 GHz i5 Macbook Air, 4 GB memory, OSX 10.8.2, MS Office for Mac ver 14.2.4
My current folder size is over 40gb, theres one identity folder which occupies 9gb data which i think is the main since it says its last opened/modified one. while the rest which i think its not important uses 4-5gb (each extra identity folder contains atleast 4-5 gb data and i have around 6). Is it ok to delete those and keep the main one?