Outlook 2003 introduced a new file format for the message store. It supports Unicode formatting and has no limitation in the number of items per folder or in the size of the PST. This is commonly called a Unicode PST.

The old format, now officially called "Outlook 97-2002 Personal Folders File" and commonly known as ANSI PST, has a limitation of up to 65,000 items per folder and an overall PST size of 2 GB. (If the PST was created in the oldest versions of Outlook, the number of items per folder was as low as 16,000.)

How to Determine if a PST is using ANSI or Unicode Format

Because of the large file size support, it's highly recommended that you upgrade to the Unicode PST format, however, Microsoft does not offer a tool that upgrades the PST, other than what is built into Outlook: Import/Export.

Normally we feel Import/Export is a poor choice when moving PSTs, except under specific and limited situations. Converting your PST to a Unicode PST is one of those times when using Import may be the best way.

There are three methods to do it yourself and one third party tool available to make the conversion. In all cases, it's not a true conversion - a new PST is created and your items are moved or copied to the new PST.

Methods 1 and 2 are best used with new profiles or existing profiles if they were created in Outlook 2003 or 2007. Method 1 (Import) copies every thing over to the new PST, Method 2 (manual move) is better if you want to control what is moved, keeping old items in the ANSI PST and only moving items you need going forward.

If you upgraded your version and are using a profile created in Outlook 2002 or earlier, Method 3 (archiving) is generally better.

If you are using a language such as Hebrew, Arabic, or Asian, and the font in your messages is a question mark or other symbol, try Importing (Method 1). Do not add the pst to your profile using File, Open, Outlook Data File. If Importing does not result in readable messages, you may need to contact Microsoft Support for resolution.

Make a copy of your ANSI PSTs before using any of the methods. Most of the options move the items to the new PST and if something doesn't work and you want to re-try it, you'll need another copy.

Methods: Import | Manual | Archive | Tools

Method 1: Import

This option imports copies of the items; it does not move them. The modified date on each item will be changed to the date of the import. This method works well for a large number of users and is best with a new computer with Outlook 2003 or 2007 either pre-installed or installed after purchase (not upgraded from an earlier version).

This method allows you to filter messages (importing only newer ones for example) or import items in specific folders (such as only contacts and calendar). Note that if you are only moving items in specific folders, Method 2 may be better.

1. If upgrading from an older version of Outlook, create a new profile. This will create a new Unicode PST and set it as your default delivery location. If this is a new installation of Outlook 2003 and up, continue to step 2.
2. Make a copy of your ANSI PST.
3. Go to File, Import and Export. (File, Open, Import in Outlook 2010/2013)
4. Select Import from another program or file.
5. Select Personal Folder File (pst) - press P twice to locate it.
6. Browse to the PST you want to import and complete the wizard. If the PST is large it may take several minutes to complete.

Keep in mind that when you import, you change the last modified date (so autoarchive won't work as expected) and published forms and custom views will not be imported to the new pst.

Method 2: Manual

This method is slower and best suited for PSTs with fewer folders, although it works pretty good if you have a large number of subfolders, since you can move them in one group. This is a good method to use if you are moving to a new computer as it works best with a new profile.

1. Make a new profile in Outlook. This will create a new Unicode PST and set it as your default delivery location.
   I recommend that you do not check for new mail until you have the items moved into the new PST. If you have mail in the Inbox, move it to a new folder called "New Mail" until you are done moving the ANSI items over.
2. Make a copy of your ANSI PST.
3. Connect the ANSI PST to your profile.
4. Move or copy the items in the ANSI PST to the new PST. I prefer Move because you can see what's been moved but you should definitely make a copy of the PST before doing this.
   If you have a lot of folders and plan to retain the same folder structure you can drag the top folder and all contents, including subfolders, will be moved.
5. When your are done moving the items, right click on the ANSI PST and choose Close 'this personal folder' from the menu.

Using Move will preserve the last modified dates. If you move entire folders, published forms and custom views for those folders will moved to the new pst.

 

Video Tutorial

This video tutorial shows you how to create a new data file in Outlook 2010 (or 2007/2013). The steps are similar in older versions.

Method 3: Archive

This method is best if you upgraded from a previous version and kept your old profile. It is highly recommended that you have a backup of the ANSI PST as messages are moved when you use Archive. Also note that flagged itemscan't be archived - you'll need to move them to the new PST or remove the flags before archiving.

1. Create a new Unicode PST file in Tools, Options, Mail Setup, Data Files dialog or Files, Data File Management (Outlook 2003/2007). In Outlook 2010/2013, create a new pst in File, Account Settings, Data Files.
2. Choose Add. A Unicode PST is the top option "Outlook Personal Files Folder (pst)" Complete the dialogs and return to Outlook.
3. Choose File, Archive.
4. Select the root of your current ANSI PST folder (this is the Outlook Today folder) in the Archive dialog.
5. Set the date to tomorrow.
6. Check the Include items with "do not Autoarchive checked" option at the bottom of the dialog box
7. Select your new Unicode PST as the folder to archive to.
8. Click Ok and Outlook archives all items from the ANSI PST to the Unicode PST (this moves all messages from your ANSI PST to the new one).
9. Make the new PST your default PST. File, Data File management, select the new PST and click the Make Default button.
10. Delete the ANSI PST from your profile.

After making the new PST your default delivery store, you need to verify the contacts folder is set as an address book. Right click on the Contacts folder and choose Properties. The Address book tab should have a check box to enable the folder as an address book.