From the Outlook Express menu select Tools | Options | Maintenance and click the StoreFolder button. You see a dialog with the name of the directory that has your mail files. If you look in that directory you find files named after your mail folders and news groups. They all have a .DBX suffix. Outlook Express keeps all messages in these database files. If you make copies of these files regularly, you\’ll have a safe backup of your OE mail. 

Restore (if necessary): To restore the backup data, just copy it back to the directory. You can selectively restore folders by just copying specific files back. Alternatively, you can use OE\’s File | Import | Messages feature to import one or more of the backup folders. Email Account Settings

As far as we know, the procedure works for all kind of email: The regular SMTP / POP3 based email, MAPI, IMAP or even the free Hotmail Account, that is built into Outlook. For Hotmail, however, some messages and settings might be stored only at the Hotmail server ( = somewhere at Microsoft !) and not on your local PC.