How do I Compact Folders in Outlook and Why?

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...  Your Outlook data is stored on your computer in one or more "personal folders", usually called .PST files. (the .pst refers to the file extension assigned to these kinds of files)  Every Outlook data item (email message, task, contact, etc.) occupies space in a .pst file.

[ Compress Image ]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 or delete a message from it? 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 data file as well. But the space it occupied is still unavailable for other uses in kind of a virtual hole in the data file. 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 same process happens when the automated "Auto-archive" process moves messages out of one PST file and into the Archive file.

This is why you need to occasionally compact your 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 and open faster.

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.

How long will this process take?

It really depends on how many "holes" are in your data file but it could take just a few seconds or even all night long.  I recommend that once the process starts that you let it finish.  If you haven't ever done it then prepare that it could take quite a while.  You cannot use Outlook while it is running, but you can switch to other programs and do other tasks while it is running.

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. (if you have a very large file, it could take a very long time)
  4. When done, click OK, then Close.

The .pst file is now compacted. Repeat as desired for additional .pst files.

Compacting for Outlook 2007 and 2010

Compacting .pst files in Outlook 2007 and Outlook 2010 is a little different than in previous versions. Just follow these steps and you'll have no trouble:

  1. Click File, then (Office 2007) Data File Management or (Office 2010) Account Settings. This opens the Account Settings dialog box, make sure that your on the "Data Files" tabbed section.
  2. Select the .pst file you want to compact. (You can start at the top and work your way down)
  3. Click Settings. This opens the Settings dialog box for the selected .pst file. (You can also double-click on it)
  4. Click Compact Now. (if you have a very large file, it could take a very long time.  Do not Interrupt it, let it continue)
  5. When compacting is done, click OK, then Close.

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