Using Outlook express you can open it.
DBX folders have names corresponding to their email mailbox. For example, common names are Inbox.dbx, Sent Items.dbx, Drafts.dbx, and Deleted Items.dbx. Folders.dbx stores the master index for all the mailboxes. If it is missing, Outlook Express will re-index the mailboxes and recreate it.
DBX mail folders can be imported into Windows Mail (included with Windows Vista) by selecting , then choosing and selecting the DBX folder you would like to import.
DBX folders can be imported into Windows Live Mail (included with Windows 7) by selecting and locating the appropriate DBX folder.
NOTE: DBX folders should only be opened in Outlook Express or imported using another program. If opened or edited manually, they can become corrupted and cause Outlook Express not to function properly.