Email not appearing in list, but files exist on disk

[francis picabia]

We've been running Cyrus imapd for many years and it is normally robust.

It is now on Redhat 5.8, using local storage.

A support call reported that in the webmail summary view, there
were over 130 unread messages, and yet the message list
could show only 8.  The messages showing are the most
recent received since Aug 28.  I checked the disk files and
there were about 130+ files in the top level
of this mailbox.

I su'ed to cyrus and did :

/usr/lib/cyrus-imapd/reconstruct -r -f user.USERNAME

where USERNAME is the account name.

I checked again in webmail (had logged out, back in) and
no difference, still only the same 8 emails showing.

I thought I should try another email client in case the webmail
client had problems digesting something.

I set up my Linux Thunderbird to connect to this account over IMAP.
It showed only 8 emails as well.

I looked again at the files on disk, and now it jived - only 8 messages
on disk.  At first I thought reconstruct had messed it up, but
I can see the IMAP connection from Thunderbird also had
a role.

Looking in the imap logs, I found:

Aug 30 14:47:20 myserver imap[30180]: Expunged 124 messages from user.USERNAME

The 30180 thread corresponds to my Thunderbird client.  It must have
done an expunge on connect and somehow these messages
were thought to be marked for deletion by cyrus.

I am currently recovering the lost email files from backup tape, and I'll
do some additional attempts to reconstruct with a copy of those
files.  Are there any suggestions on how I go about a recovery of
this mailbox so it is true again?