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  • Outlook PST files

See Also:

• http://support.microsoft.com/kb/830119
• http://email.about.com/od/outlooktips/qt/et_archive_mail.htm

Microsoft Outlook stores your local email in a file with a '.pst' extension, often called a PST file. The main PST file used by Outlook is called Outlook.pst by default - this is where all your incoming email is stored. If you have a lot of email, the PST file can grow very large (e.g. bigger than 2 GB) and cause your Outlook to slow down, as well as providing a particular challenge to your OnTheNet backup.

Briefly, the challenge for your OnTheNet backup is that the backup looks for files that have changed since the last time it was run, then looks for changes within those files so that it can send just the changes over your internet link - this makes the backup much faster than if it were to simply send the whole file. When you receive email the changes are largely all near the end of the PST, but the backup has to scan the whole file looking for the changes. With a large file this scanning can take some significant time, which means you backup may take much longer than otherwise.

Outlook itself is configured by default to automatically archive your older email to a file called Archive.pst. This helps your main Outlook.pst stay a reasonable size, however, again depending on how much email you actually have, this can simply move the problem from Outlook.pst to Archive.pst. In the worse case this can actually make things worse for your backup as the Archive.pst can get very large, and now the backup needs to scan both the Outlook.pst and the Archive.pst.

The recommended practice is to keep your older emails in an Archive-YYYY.pst PST file, where the 'YYYY' is the relevant year, e.g. Archive-2010.pst, Archive-2011.pst. This means your Outlook.pst stays a reasonable size, and the archive PST files only grow to a limited size.

If you already have a large (e.g. bigger than 2 GB) Archive.pst file, you can simply rename it to Archive-YYYY-MM-DD.pst, where YYYY-MM-DD is the current date, e.g. Archive-2011-05-12.pst. reducing the number of emails in your main PST file and thus reducing the size of the main PST file. This has the dual benefit of both making your Outlook faster (because it doesn't have to deal with all the old emails) as well as making your backup faster.

Depending on which version of Windows and Outlook you have, your Outlook PST files are usually in one of these locations:

drive:\Documents and Settings\\Local Settings\Application Data\Microsoft\Outlook
drive:\Users\\AppData\Local\Microsoft\Outlook\