Delete the contents of the ''Deleted items folder'', each time you close down OE.
Goto Tools > Options then the Maintenance tab, and tick the first option to do this automatically.
Recently, everytime I close down Outlook Express, I get a popup window offering to "compress my messages." The last time I did that, I found my old messages were now blank. Since I don't see anyway to uncompress messages, I assume they're gone forever.
I deleted all my "deleted" messages (which were several hundred" and I still get this annoying popup. Anyway to get rid of it besides compressing my messages?