I have looked at the threads about disappearing emails but none really
apply to my case. In the past 5 days, I have seen thousands of emails
disappear. This happened in multiple folders, but I never lost every
message, only most of them in those folders. This has never happened
before.

Just to be clear, here are some of the precautions I normally take.

1. I keep my inbox relatively small. I have folders like
"OldInbox2005" to do that. Same for sent items, e.g., "OldSent2007".
--- But I just saw my OldSent2007 folder go from 51MGB to 2MB,
leaving an apparently random subset of the emails intact. That is my
largest file. OldSent2005 went from 7MB to 137KB.

2. I frequently compact all my Outlook Express folders.

3. Antivirus, firewall, anti-adware all kept up to date.

4. I do regular backups. That's how I know this all happened since
1/12/08, the last backup of my Outlook Express folders.

5. I just restored that 51MB OldSent2007 from the 1/12/08 backup and
it seems to be fine. I compacted it and also shut and reopened OE.
Still looks fine.

Any one have any ideas about this?