How to Force Outlook to Use Unicode File Format

In 2003 and above, Outlook file size limit is 2TB.However, if you upgrade from 2002 to 2003 or 2007 and do not make a new Outlook file and import your old data, it will stay in ANSI format.

The proper way to upgrade is to create a new profile in Outlook and import old data.

By default, Outlook will create a Unicode personal store when possible. The exception is when creating PSTs for use with IMAP (Internet Message Access Protocol) or Hotmail/MSN accounts, as those accounts require ANSI.

Administrators may want to prevent users from adding these accounts types to Outlook by forcing the use of Unicode PSTs only. Other administrators may want to force Outlook 2003 to only create ANSI PSTs to insure backwards compatibility with older versions still in use on the network.

Either is accomplished by setting a registry value for NewPSTFormat. As always, use extreme care when modifying the registry and if you're not sure what you're doing, don't do it!

To force Unicode or ANSI PSTs, navigate to HKEY_CURRENT_USERSoftwareMicrosoftOffice11.0Outlook
Add the NewPSTFormat value with one of the following values:

Prefer Unicode PST: 0 (default)
Prefer ANSI PST: 1
Enforce Unicode PST: 2
Enforce ANSI PST: 3
By using a value of 2 or 3, you can restrict all new .PST files to either the old format or the new format

ANSI refers to the older type that's limited to 2GB. When you use Unicode, you'll be able to have a PST file larger than 2GB.