Administration settings disappeared / are not saved. Why?

This means Internet Guest Account on your server has insufficient permissions to the WebMail data folder (its location is specified in web.config file). Please complete the steps below to grant the appropriate permissions:

• using Windows Explorer, navigate to the folder which contains the data folder;
• in context menu, choose "Properties" of the data folder and "Security" tab;
• add Internet Guest Account (usually IUSR_) into the list;
• tick "Allow full control" checkbox to grant permissions and press "OK".