How do I make an Outlook PST file smaller?

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My Outlook PST file is huge! It takes forever to back up, and is just generally incredibly unwieldy. How can I make it smaller?

Outlook PST files are Outlook’s repositories for email, contacts,¬†calendar information, and much more. (Not to be confused with Outlook.com or Outlook Express – those are completely different and unrelated products.)

Outlook PST files can become very, very large if you’re not paying attention, and practical considerations like speed and backups often make us¬†want to control the size well before reaching that stage.

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