You can change the email format of your local mail folders to one of the following email formats:
If a problem occurs when you convert from one format to another, you might not be able to recover your data.
To change the email format of a local mail folder, perform the following steps:
Right-click on the folder whose format you want to change, then choose Properties from the popup menu.
Select the email format that you require from the New store format drop-down list in the Reconfigure dialog.
If you want to index the contents of the bodies of the messages in the folder, select the Index body contents option.