To resolve the issue of missing or disappeared emails after a system crash or error, here are a few things to try:

1. Check Deleted Items Folder: Check if any emails have been moved to the Deleted Items folder. Messages deleted from the Deleted Items folder can’t be recovered.
2. Check Junk Email Folder: Check if any emails have erroneously been marked as spam and moved to the Junk Email folder.
3. Enable Cached Exchange Mode: Enable Cached Exchange Mode to ensure that all emails are cached and accessible via Outlook.
4. Disable Add-ins: Disable and then reenable Outlook add-ins to ensure that incompatible or corrupted add-ins are not causing the problem.
5. Reinstall Outlook: If all else fails, reinstall Outlook to ensure the program is running correctly.