Helping people with computers... one answer at a time.
I occasionally get reports of people who've lost the contents of their inbox. We'll look at a couple of common causes and resolutions.
The contents of my inbox disappeared! Can I recover?
I've received this question more than once about both Outlook and Outlook Express. There isn't enough information in the questions to pull together "The Answer", but there are definitely a number of things to look at when your email or the folders containing it disappear without warning.
To answer the question directly: maybe. Depending on what happened your mail, like the truth, may still be out there.
One common confusion for both Outlooks under Windows 2000 and Windows XP is that each Windows user account gets their own set of Outlook Express mail folders by default. So if you use multiple accounts in Windows, it's possible that you're simply logged into a different account, and looking at a different set of folders.
Because Outlook and Outlook Express are completely different programs, and each has some unique set of issues to look at.
Outlook Express also has the concept of "Identities" which is another way to manage multiple users with separate email accounts without requiring different Windows accounts. Make sure you're using the identity you think you are.
Even if you're not using multiple accounts or identities it's a good idea to search your hard disk for additional "message stores", the place where Outlook Express keeps your folders. Use Window's "Search for Files or Folders..." feature to look for "*.dbx" files. The directories in which you find those files are other message stores that Outlook Express has used. Knowing where they are you can now import their contents into your current mailbox if you wish.
If you're running an anti-virus product Microsoft Support has a Knowledgebase article Outlook Express E-Mail Messages Are Missing from the Inbox Folder which discusses an interaction with McAfee VirusScan that can cause the problem.
Depending on your symptoms the KB article Folders Do Not Appear in the Local Folders List may also be helpful.
Also, see below for some more things to look at that apply to both Outlook and Outlook Express.
Outlook supports what are called "Profiles" which are roughly equivalent to Outlook Express's "Identities". In Outlook's case they can be managed through the Windows Control Panel's "Mail" options. Typically there's a single default profile but you can also configure Outlook to ask which profile it should use each time it starts up. Make sure you're using the profile you expect.
Outlook includes a feature called "auto archive" which will automatically move mail items older than a certain amount to an archive folder. Select the Tools menu, Options, Other, AutoArchive and check the settings displayed. It is possible to configure auto-archive to move or delete items without prompting you, so double check the settings. If it's moving items to an archive folder this dialog will also show you where that folder is located.
As with Outlook Express, it's a good idea to scan your hard disk for additional message stores. Search for "*.pst" and "*.ost". These files (not directories) contain the email folders managed by outlook. You can simply use Outlook's File menu, Open, Outlook Data File... to see what they contain.
Outlook includes support for Exchange Server. If you are using Exchange Server based email then your email is typically stored on the server and not on your local machine. Be aware that rules and policies on the server could cause email to be archived or removed without notification. Check with your Exchange administrator to see if that might be the case.
Both Outlook and Outlook Express
Another very easy trap to fall into that might cause messages "disappear" is to simply have an improper view applied. Both Outlook and Outlook Express have the ability to show only messages matching certain criteria. For example "show only unread messages" is a common setting; once you read the message it "disappears". Applying a different view that doesn't restrict which messages are shown causes the message to reappear. Check the View menu in either application (and the Arrange By sub menu if present) to see what your current settings are. If they're restrictive it's possible your mail is still there, just not in view.
If your email accounts are IMAP accounts rather than the currently more common POP3, then your email is by default stored on the mail server and not your local machine. Much like Exchange Server, server-side policies could affect the contents of your mail folders. Be sure to check with your mail administrator.
I have experienced cases where poorly designed backup utilities can get confused if Outlook or Outlook Express are running at the time the backup is performed. The email programs keep their mail files open, preventing the backup programs from actually backing them up. In the worst case scenario (which I experienced) this can cause the backup program to attempt to restore the files to an older previously backed up copy, resulting in disappearing email. The safest thing is to know when backups are scheduled to happen and ensure that Outlook and Outlook Express are both closed prior to that time.
Finally, there is the possibility of corruption. Typically either of the Outlooks will complain if the email files become corrupt in some way. Outlook Express may try to recover but often requires that you simply rename the corrupt folder and allow Outlook Express to build a new one. Outlook comes with the "scanpst.exe" tool that will attempt to repair Outlook's PST files (use Windows Find Files or Folders ability to locate it -- various versions of Office install it in different locations).