This policy setting allows .OST files to silently update to Unicode format from ANSI. If you enable this policy setting, ...

This policy setting allows .OST files to silently update to Unicode format from ANSI.

If you enable this policy setting, it will only have meaning if the related policy setting "Exchange Unicode Mode - Ignore OST format" is enabled and set to the options listed below.

The behavior is as follows -

"Ignore OST Format" policy setting is enabled and set to "Create new OST if format doesn't match mode"; "Silent OST Format Change" policy setting is enabled:
If Outlook detects a mode that is different than the current .OST mode, then a new .OST is created without prompting the user.

"Ignore OST Format" policy setting is enabled and set to "Prompt to create new OST if format doesn't match mode"; "Silent OST Format Change" policy setting is enabled:
If Outlook detects a mode that is different than the current .OST mode, the user is prompted to allow a delay in the conversion to the mode set by policy.  By clicking Ok, a new OST is created without a prompt for a new .OST name.

If you disable or do not configure this policy setting, users will be prompted to enter a new name for the updated .OST file.