Outlook Express Files: (The following information applies to Outlook Express 4.0 and earlier versions:) Outlook Express stores the list of your e-mail "folders" (such as Inbox, Outbox, etc.) and the mailbox filenames they use in a file called FOLDERS.NCH. In that file is listed each folder and the MBX and IDX file used by that folder. MBX files store the text of your e-mail messages as fairly normal ASCII text. IDX files store the destination/source addresses and subject lines of your e-mails. For each of your e-mail folders, there is an MBX file and an IDX file. (For example, your Inbox uses INBOX.MBX and INBOX.IDX.) You can also save individual e-mail messages as a single file containing a single message, which would have an .EML extension. (The following information applies to Outlook Express 5.0 and later versions:) With OE5, Microsoft totally revamped the structure of how OE stores e-mail. For starters, there is no longer any FOLDERS.NCH file. E-mails are no longer stored as plain text, but rather in a binary file with a DBX extension which cannot be easily read. (Not with a normal ASCII text editor, anyway, although there are utilities available on the Internet to extract messages from DBX files.) Each folder now has its own DBX file, for example INBOX.DBX and OUTBOX.DBX. There is also a file called FOLDERS.DBX which stores folder info and the names of the DBX files for each folder. (Obviously, FOLDERS.DBX has replaced FOLDERS.NCH.) (Note that in some beta versions of Outlook Express 5, the folder storage files used an .ODS extension instead of .DBX.)