Mail file maintenance

Many Outlook and ClearContext issues and performance problems are the result of a corrupted or over sized mail file. Here are steps to check for and repair corruption and keep your mail file size in check:

1. Rebuild your mail file

This method is recommended for users with Exchange Mail accounts. If you are not sure, or are using a different email account type, use the alternate method in the next step 1b.

  1. Go to the Outlook File > Account Settings screen

  2. Click on the Data Files tab

  3. Select the mail file for your main email address, then click the button to Open File Location

  4. Optionally, disable ClearContext in the Outlook Add-ins screen, as this may speed up the rebuild process

  5. Shut down Outlook

  6. In the File Explorer window opened from step 3, find the mail file from that step that is an OST type or "Outlook Mail File", and rename it to something else like "backup.ost"

  7. Restart Outlook and wait for the status bar on the bottom to indicate that all folders are up to date. Depending on the size of your mail file, and connection speed, this could take some time, but Outlook will be usable but potentially slow during this process.

  8. Optional but recommended. Check that the mail configuration is set to cache all mail data, instead of the default one year. See Exchange Configuration for details.

1b. Alternate method to check for and fix errors in your existing mail file

*** If you have performed step 1 above, this step is not necessary ***

Close Outlook and run Microsoft's SCANPST utility against your mail file:

  1. Find SCANPST via Programs > Accessories > System Tools or use Start > Search or Start > Find to locate it on your hard drive. (OR use the Microsoft Fixit tool in this KB article to find and run SCANPST).

  2. Once open, you will need to find the location of your Outlook mail files. The default location for your Outlook mail file is in Outlook's local settings directory: C:\Users{USER_NAME}\AppData\Local\Microsoft\Outlook.

    Another way to find the mail file location is to go into the Outlook Accounts page, click on the Data Files tab and view the mail file properties.

  3. Scan your primary outlook.OST (Exchange) or outlook.PST (POP) mail file and allow it to repair any issues it finds.

  4. Repeat this process until SCANPST no longer reports errors. We recommend performing the same process on any PST mail files connect to Outlook and used with ClearContext as well.

2. Use archive to get your mail file size down

Use archive to keep your primary mail file size below 1 GB. To check your file size, right click it in your Outlook folder list, select Properties and click Folder Size. We suggest you archive by date:

  1. Select File > Archive from the Outlook menu.

  2. Under Archive this folder and all subfolders, click your primary mail box.

  3. Select a date after Archive items older than. We suggest 6 months or less.

  4. Select an archive file. Outlook will suggest archive.pst in your Outlook local settings directory. Remember the location of this file.

  5. Click OK and Outlook will move your messages from your primary mail file to the archive file. Watch the status of this process in the bottom right hand corner of Outlook.

  6. If the file is not visible in the Outlook folder list, open it via File > Open > Outlook Data File.

  7. Once complete, compact your primary mail file to further increase performance.

Repeat this process on a regular basis to keep your mail file healthy and performance snappy.

3. Create a new profile in Outlook and start with a fresh mail file

If you have tried the above and are still experiencing issues, try using a fresh new mail file as your primary mail file. The easiest way to do this is to close Outlook and create a new profile via the Windows Control Panel. In recent versions of Windows navigate to User Accounts and then select Mail. One can also search for "mail" in the Control Panel search box.

Exchange Users

When you first first open your new profile, Outlook will rebuild your mail file from scratch. Expect performance to be slow until Outlook updates all folders.


Once you get your new profile up and running, your mail file will be empty. Add your old mail file as a separate data file via File > Open > Outlook Data File. It's likely called outlook.pst or some variation in the default Outlook local settings directory. You can also use File > Import & Export to import your old messages into the new mail file.

Last updated on Apr 22nd 2022