When you say you permanently deleted an email from your .OST file, what do you mean? If you hard-deleted the email from a folder in Outlook which was NOT your deleted items folder, you will have to change the registry to allow you to recover from those folders. If you deleted the email from your deleted items folder, there is a much simply way to recover it.

Either way, the following link provides instructions:

https://support.microsoft.com/en-us/kb/246153