PST File Overview

Outlook data is stored in a single file called a Personal Folders file, or Personal Store (PST). Over time, this file can grow exceedingly large as more and more data accumulates. When the size grows we have to back up the PST file or move it to another computer; or until you start to run out of room on your hard drive and realize that your Outlook data store is consuming a huge chunk of space. At this point, you need to know how to safely trim the size of this file and will probably also want to understand how to keep the file from growing this large again. The steps provided here show you the likely causes of this PST file's unnecessary girth and how to keep the file slim and trim in the future.

How to Fix It
The first step is to find out which Outlook folders are taking up the most room.

1. In the Folder list, right-click Outlook Today.
2. Click Properties For Personal Folders.
3. Click Folder Size.
4. Scroll through the folders and identify the largest ones. You'll typically find that Deleted Items, Sent Items, and Inbox are the largest folders.
5. You can free up space by permanently deleting items in Deleted Items, much like emptying the Microsoft Windows® Recycle Bin. But make sure you really want to do this—you can't get these messages back after you empty the Deleted Items folder.
6. Right-click Deleted Items in the Folder list or Outlook bar.
   Click Empty Deleted Items Folder.
7. Click Yes when prompted if you're sure. The fastest way to trim your personal folders file is to archive or delete what you don't need. Archiving data removes it from your folder and puts it in an archive file so that you can retrieve it later if you need it. Archiving works with an archive date—sort of a pull date for old items. You can manually archive the data whenever you feel like it or you can use the Outlook AutoArchive feature to schedule archives on a regular basis. You can also use these same procedures to delete items older than the archive date. Here are the steps to repeat for each of your largest folders to manually archive or delete old data in them. If you'd rather set up the folders to be automatically archived, skip to step 14.
8. On the Outlook File menu, click Archive.
9. Select the Archive this folder and all subfolders check box.
10. Select the folder you want to archive in the folder list box.
11. Click the drop-down arrow on the Archive items older than field, and choose a date (Figure 1).
12. Optionally click Browse to pick a file other than the default archive file.
13. Click OK to begin the archiving. To add a folder to the list of AutoArchive folders so that it'll be archived automatically, follow these next steps for every folder you want to archive. Then continue to perform an immediate AutoArchive on these files.
14. Right-click on the folder and click Properties
15. Click the AutoArchive tab.
16. Select the Clean out items older than check box.
17. Set the amount of time to leave messages in your Inbox folder. This is set to six months by default.
18. If you'd rather delete these items than archive them, select Permanently Delete Old Items. Be sure you want to do this, however, since you can't retrieve them.
19. Click OK. Once you've set up all the folders you want to archive automatically, you can run automatic archiving immediately instead of waiting for the specified cycle time to elapse, as follows:
20. On the File menu, click Archive.
21. Select the Archive all folders according to their AutoArchive settings check box.
22. Click OK. Finally, after removing all the items you want from the personal folders file, you need to compact the file to make it smaller.
23. Right-click the Outlook Today icon in the Outlook bar or the Personal Folders folder in the folders list.
24. Click Properties For Personal Folders.
25. Click the Advanced button.
26. Click the Compact Now button.