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Tip: Reduce the Size of Outlook’s Offline Data File (.ost)

I use Outlook extensively and with my version of Outlook 2010, I started noticing some problems lately.  I do a lot of search in multiple large folders and the search started to become slower and even freezed Outlook.  I use Outlook in offline mode, so that I have a copy of all messages locally, as well as on our Microsoft Exchange Server.

After some more research, I found that the .OST file is quite large: in fact, as much as 2 times larger than the .PST file generated for my account.  I know that I recently removed thousands of old emails contained multiple folders that were no longer necessary and put them in an archive file.  In theory, this should have cleaned the offline storage, but the file is still large (this even if you empty your Deleted Items folder).

I found out that there is a "Compact Now" feature that makes this process of cleaning and reducing the size of the .OST file locally.  To use it:

- in Outlook (2010), click File
- click Account Settings
- click on the Data Files tab
- select the appropriate data file you want to compact, then click Settings
- click the Advanced tab
- click Outlook Data File Settings
- click Compact Now

Once you start the process, you will need to be patient if you have a large file (2Gb took about 20 minutes). Using this feature literally reduced in half the size of my.OST file.  I also now notice faster access time in my Outlook.  I believe that running this every 6 months is a good way to keep your Outlook lean!

For more detailed information, refer to Reduce the size of Outlook Data Files (.pst and .ost).