Why Compact PST (Outlook Data) Files?

You're probably wondering, "What does it mean to compact Outlook data files (usually called Outlook PST files), and why should I do it?" Let me tell you the story...

Unless all your stuff lives on an Exchange server somewhere, your Outlook data is stored on your computer in one or more personal folders files, usually called .pst files.

The .pst refers to the file extension assigned to these kinds of files.

Anyway, every Outlook data item (email message, task, contact, etc.) occupies space in a .pst file. So far so good.

So what happens to the .pst file when you delete an Outlook item? The item goes to Outlook's Deleted Items folder. Since the item can be recovered from there, it makes sense that the item still takes up some space in the .pst file.

Now what happens when you empty the Deleted Items folder? From our point of view, the item is completely gone. It can't be recovered using any normal means. And the item is deleted from the .pst file too.

But the space it occupied is still unavailable for other uses.

This means that, unless something happens, your .pst files will get bigger and bigger over time, even if you keep the same number of items in Outlook.

This is why you need to occasionally compact PST files. Compacting Outlook data files reclaims the space that is unavailable because it was previously occupied by an item. This can greatly reduce the amount of space that the .pst file occupies on your hard drive, and helps Outlook function efficiently.

How Often Should I Compact My .pst Files?

There are no hard and fast rules for this. Unless you are having problems, such as Outlook running very slow, or are in desperate need of more disk space, I would suggest you compact PST files once or twice a year.

Compacting for Outlook 2003

To compact a .pst file in Outlook 2003, follow these steps:

  1. Click File. In the File menu, click Data File Management. This opens the Data File Management dialog box.

  2. Select the .pst file you want to compact, then click the Settings button. This opens the Settings dialog box.

  3. Click the General tab, then Compact Now.

  4. When done, click OK, then Close.
The .pst file is now compacted. Repeat as desired for additional .pst files.

Compacting for Outlook 2007

Compacting .pst files in Outlook 2007 is a little different than in previous versions. Just follow these steps and you'll have no trouble:

  1. Click File, then Data File Management. This opens the Account Settings dialog box to the Data Files tabbed page.

  2. making sure that you are working on the Data Files tabbed page, select the .pst file you want to compact.

  3. Click Settings. Settings and other options appear above the list of .pst files. This opens the Settings dialog box for the selected .pst file.

  4. Click Compact Now.

  5. When compacting is done, click OK, then Close.

And that will do it. Repeat as desired for additional .pst files.

You now know the basics of PST (personal folder) files. From here you can: