With a fresh install of the latest eMail block, the course folders user preference is not enabled.

To reproduce:

1. Make sure the admin block setting for 'email_marriedfolders2courses' is set to yes.
2. As a user, go into email and click on 'Settings'.
3. Change the course folders option to 'yes' and save changes.
4. Go back to the Settings page - notice that the option has reverted to 'no'.

The email_preference table in the database is missing the marriedfolders2courses field, and the email_folder table is missing the course field.

A patch to install.xml is attached.