If your PST files have become very large and Outlook is slowing down, or you want to shrink a PST file without Outlook, then I would recommend that you try DataVare Outlook PST Compact Expert Tool. I have used it myself, and this tool easily compresses PST files even without Outlook installed. It also allows you to save space by removing attachments or saving them in a separate folder. The user interface is very simple, and many PST files can also be compressed simultaneously in batch. If you are troubled by Outlook slowing down again and again, then definitely try this tool once. It will save you a lot of time and space.