Migration considerations
Even though several new features and user interface changes are added in Outlook 2010, the Outlook data files (.ost and .pst) and Outlook profile file (.prf) formats in Outlook 2010 are compatible with earlier releases.
Outlook data files (.pst and .ost)
With Outlook 2010, users can open and use Outlook data files that were created in earlier versions of Outlook. Users who have Outlook data files (.pst) can continue to use the files without converting or migrating the files. Users whose Exchange accounts are configured to use Cached Exchange Mode have offline Outlook data files (.ost). You do not have to re-create these .ost files if you perform an in-place upgrade to Outlook 2010.
Note that moving .ost files between computers is not supported. Therefore, you should not manually copy .ost files between computers. Additionally, the User State Migration Tool (USMT) cannot be used to migrate .ost files.
By default, Outlook .pst and .ost files that are created by using Office Outlook 2003 through Outlook 2010 are in the updated Unicode file format that allows for larger file sizes (the 2-gigabyte (GB) limit is eliminated). The non-Unicode ANSI data file format s also supported by Outlook 2010.
If users currently have non-Unicode ANSI-formatted .ost files, we recommend that you upgrade the .ost files to Unicode.
Outlook profile file (.prf)
As in earlier versions of Outlook, you can continue to use the Outlook profile file (.prf) to provide options for specifying additional Outlook settings or MAPI services. The Outlook 2010 .prf file format has changed but Office Outlook 2007, Office Outlook 2003, and Outlook 2002 versions of the file will work with Outlook 2010. If you plan to make updates to the .prf file for an Outlook 2010 deployment, we recommend that you re-create the .prf file by using the Office 2010 Office Customization Tool (OCT), export the settings to a new .prf file, and use that file to specify the additional Outlook settings or MAPI services that you want.
Reverting to Office 2007 from Office 2010
Because of the changes in Outlook 2010 that enable multiple Exchange e-mail accounts, user profiles that were upgraded to Outlook 2010 will not work if the user removes Outlook 2010, reinstalls Office Outlook 2007, and then attempts to start Office Outlook 2007 by using the same user profile. In this scenario, the user profile must be removed and re-created in Windows through the
Control Panel and
Mail options.
VBA settings migration
In Office 2010, Visual Basic for Applications (VBA) 6.0 is updated to VBA 7.0. VBA 7.0 settings are reset to their defaults after migration instead of automatically repopulating. This occurs because the registry settings for VBA are in a different hive in Office 2010, as shown in the following table.
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