OE mails disappeared

[Malta Soron]

My father’s got a problem: a whole bunch of his mail just disappeared. He discovered it just after I made the backup, so that’s no solution. The problem works like this: he has a lot of folders in Outlook Express in which he stores e-mail he wants to save, but doesn’t look at a lot. This afternoon he suddenly discovered that a lot of e-mails are missing: instead of the hundreds of mails that should be present, the folders contain only a few or none at all. We asked around, but no one in the family deleted them. The folder “Removed items” (or whatever it is called in English) always gets emptied when OE is closed, so they’re not there either.
We regularly use ‘Compress folders’ (or something like that; I mean the tool by which OE decreases the size of the .dbx-files by some sort of defragmentation). Although it doesn’t seem logical to me, could that have caused the trouble?
And I checked the .dbx files: one of the empty folders is still 44.2MB. That looks a bit large to me.
Does anyone have an idea about how to recover my father’s e-mails? Thanks in advance.