I was using Zimbra as a POP Mail server for one of my accounts (Let's call it ABC). After upgrading to Zimbra 4.0.0 GA, I was tempted to use its Web UI for this account.
I changed the settings for ABC to IMAP from POP in the Evolution Mail client. I then clicked on Send/Receive. I got ABC in the list of IMAP accounts. I then selected all emails from the folder ABC containing the download emails of ABC; and, selected to Copy (not Move) it from there to the new folder in the IMAP account. While the transfer was on, I suffered power outage. The system was shutdown.
When electricty was restored, I restarted the system and Evolution to see that the original folder ABC was empty and no emails were in the corresponding IMAP folder.
I don't have backup of ABC! (Actually I had it one month back but lost that when I re-installed that system to evaluate latest version of Ubuntu Linux).
This is by no means related to Zimbra but I am posting this so that other users take care not to give away to carelessness like I did.
Always, always, backup your e-mail regularly.