Don't store messages in the Inbox.  It is the folder most apt to be
corrupted.  As soon as you read them move them to user created folders.
Then compact the Inbox regularly.

Go to Tools | Options | Maintenance | Store Folder and write down where OE
is storing its data.
Close OE.
Go there with Windows Explorer and move (not copy) Inbox.dbx to an empty
Windows
folder.  With Win2K, WinXP and Win2K3 it will be a hidden file.

You can use either of these tools to extract the messages from the old DBX
file:

DBXtract ($5): http://www.oehelp.com/DBXtract/  although this tool is faster
and better:
DBXpress: ($25) http://www.oehelp.com/DBXpress/Default.aspx
Do NOT extract to the desktop!
With a large file this can take a long time, so let it keep running.

The messages can be dragged from a Windows folder back into an OE folder in
OE's Folder List.