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Outlook Add or Remove Data File: Full Guide

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Outlook Add or Remove Data File: Full Guide

To add or remove a data file in Outlook, go to File > Account Settings > Account Settings, select the Data Files tab, then use Add or Remove. This manages the .pst or .ost files that store your email, contacts, and calendar items.

What Are Outlook Data Files?

Outlook uses two main types of data files:

  • .pst (Personal Storage Table): Used for POP3 accounts, archiving, and exporting. These files are stored locally on your computer and can be moved, copied, or backed up.
  • .ost (Offline Storage Table): Used for IMAP, Exchange, and Microsoft 365 accounts. These are cached copies of server data and are not meant to be moved or backed up directly.

Each data file can contain folders, messages, contacts, calendar entries, tasks, and notes. The file is essentially a database that Outlook reads and writes to.

How to Add a Data File

Adding a data file lets you attach an existing .pst or create a new one for archiving or storing old emails. Follow these steps:

  1. Open Outlook and go to File > Account Settings > Account Settings.
  2. Click the Data Files tab.
  3. Click Add.
  4. Choose the type of file: Outlook Data File (.pst) for a new file, or browse to an existing .pst file.
  5. If creating a new file, enter a name and choose a location. You can also set a password (optional).
  6. Click OK. The file appears in the folder pane on the left, usually as “Personal Folders” or a custom name.

Once added, you can drag emails into the new file to organize them. To remove it later, follow the removal steps below.

How to Remove a Data File

Removing a data file detaches it from Outlook. The file itself is not deleted from your computer, so you can re-add it later. To remove:

  1. Go to File > Account Settings > Account Settings.
  2. Select the Data Files tab.
  3. Highlight the file you want to remove.
  4. Click Remove.
  5. Confirm the prompt. The file is now detached, but the .pst remains in its original location.

If you want to delete the file permanently, you must delete it from Windows Explorer (or Finder on Mac) after removing it from Outlook. Be careful: deleting a .pst erases all data inside it permanently.

Why Add or Remove a Data File?

There are several common reasons:

  • Archiving: Move old emails to a separate .pst to keep your main mailbox small.
  • Transferring: Move a .pst to a new computer and add it to Outlook there.
  • Backup: Create a copy of a .pst and store it externally.
  • Cleanup: Remove a data file you no longer need to reduce clutter in the folder pane.
  • Troubleshooting: Detach a corrupted .pst to prevent Outlook from crashing.

For .ost files, you generally cannot remove them manually—they are recreated automatically when the mailbox is configured. However, you can disable cached mode or delete the .ost file after closing Outlook to force a re-sync.

Common Problems and Fixes

Here are typical issues users encounter:

  • “Data file cannot be removed because it is the default delivery location.” You must first set another data file as the default delivery location in the email account settings, then try again.
  • File is in use: Close Outlook and any other program that might be accessing the file (like a backup tool) before removing or deleting.
  • File is corrupted: Use the Inbox Repair Tool (scanpst.exe) that comes with Outlook. It is usually found in the Outlook installation folder.
  • Removed file still shows: Restart Outlook. If it persists, check if the file is set as the default delivery location.

How to Choose the Right Data File Type

Choosing between .pst and .ost depends on your account type:

  • POP3: Uses .pst. You can add or remove them freely.
  • IMAP: Uses .ost. You can add a .pst for archiving, but the .ost is managed by Outlook.
  • Exchange/Microsoft 365: Uses .ost for cached mode. You can add a .pst for archiving, but the .ost is not meant to be moved or backed up.

If you need to move emails between computers, use a .pst. If you just want to free up space, consider archiving to a .pst instead of removing the data file entirely.

Frequently Asked Questions

Will removing a data file delete my emails?

No. Removing a data file only detaches it from Outlook. The .pst file remains on your computer. You can re-add it later to access your emails again. Deleting the actual file from your disk will permanently erase the emails.

Can I move a data file to another computer?

Yes, for .pst files. Copy the .pst file to the new computer (e.g., via USB or cloud storage), then add it in Outlook using the steps above. For .ost files, it is not recommended—they are tied to the server account and can be recreated automatically.

Why can’t I remove the default data file?

Outlook requires a default delivery location for your emails. If the data file is set as the default, you must change the default to another data file or email account first. Go to Account Settings, select the email account, click “Change Folder” or “More Settings,” and set a different delivery location.

How do I backup my Outlook data file?

Close Outlook, then copy the .pst file from its location (usually C:\Users\YourName\Documents\Outlook Files) to an external drive or cloud storage. For .ost, you cannot back it up directly—use Export to create a .pst backup instead.

What is the difference between a data file and an email account?

An email account is the configuration that connects to a mail server (e.g., Gmail, Exchange). A data file is the local storage that holds the emails downloaded or cached from that account. One account can use one data file, and you can have multiple data files for archiving or multiple accounts.

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