Why Compact Outlook Data Files?

Let's talk about Outlook data files. What are they? Why would you want to compress them? When would you do such a thing?

Everything that you see in Outlook has to be stored somewhere. Where depends on the version of Outlook you have and how it connects to the world. Outlook will use either .pst files, .ost files, or both. 

I know those are weird sounding names. They are actually references to the extensions on the files. But you don't need to worry about that because I'll show you how to find the files and work with them. Without worrying about things like file extensions. From now on, we'll refer to them as Outlook Data Files.

Why Do I Have to Compact These Files?

Because of the way these files work, every time you add an item to Outlook, one of the data files gets bigger. But when you delete something, the file that held it doesn't automatically get smaller. They just keep getting bigger.

As you can imagine, this can lead to trouble. Bigger data files take up more room on your hard drive. Outlook takes more time to work with them. At some point, they reach a maximum size and just become too clumsy to deal with.

This is where compacting the files comes into the picture. You can tell Outlook to compact these files when they get too large. Newer versions of Outlook (2010 and later) can do this on their own under certain conditions. But you can't count on it happening when you might like it to.

Besides, compacting these files can take a while and tie up your computer while it is happening. That's why you should tell Outlook when you want it to compact data files.

How Often Should I Compact My Data 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 Do I Do It?

Are you ready to compact some data files? Cool. It turns out that the steps to do this vary slightly between the versions of Outlook. But we have you covered. Just click the link below that matches your version of Outlook to get detailed instructions.


Compacting Outlook 2010 Data Files

In Outlook 2010, you can compact both .pst and .ost files. But the procedure is slightly different for each file type. So when you are looking at the following instructions, make sure to pick the ones that match the file type!

Compacting Outlook 2010 PST Files

Follow these steps to compact Outlook 2010 PST files:

  1. Click the File tab on the Ribbon, then Info.

  2. Click the Account Settings button, then click Account Settings in the menu that appears. This opens the Account Settings dialog box.

  3. Click the Data Files tab. This displays the Data Files page.

  4. Select the data file you want to compact (it’s file name should end in .pst).

  5. Click Settings. This opens the Outlook Data File dialog box.
  1. Click the Compact Now button to compact the file. A Compacting Now message may appear while this is happening.

  2. Click OK to return to Data Files.

That file is done. You can repeat these steps to compact any other .pst files.


Compacting Outlook 2010 OST Files

These steps allow you to compact Outlook 2010 OST files. They are similar but not identical to, those for PST files:

  1. Click the File tab on the Ribbon, then Info.

  2. Click Account Settings. In the menu that appears, click Account Settings. This opens the Account Settings dialog box.

  3. Click the Data Files tab. This displays the Data Files page.

  4. Select the OST data file you want to compact.

  5. Click Settings. This opens the Microsoft Exchange Settings dialog box.

  6. Click the Advanced tab. This displays the Advanced Settings tabbed page.

  7. Click the Outlook Data File Settings button. This opens the Outlook Data File Settings dialog box.

  8. Click the Compact Now button to compact the file. A Compacting Now message may appear.

  9. Click OK to return to the Data Files page.

That file is done. Repeat these steps for any other OST files you want to compact.


You now know the basics of Outlook data files. From here you can:

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