There are suggestions in this article: http://kb.mozillazine.org/Disappearing_mail

Thanks, but the article doesn't seem to address what's going on for me. When I search for an email address that I remember used to be in the now-empty folder, the emails show up in the search (under the correct folder name in "Folders" on the left side of the screen). But when I click on one of the emails found by the search (that I know used to be in that folder), no email opens... there's a blank. Any thoughts? Thanks for your help!

The global search database is clearly not in synch with what is actually in your folders. It is showing an out of date search. Fixing the global search is simple enough, but I would expect the fixed search to not even locate those emails as you have already stated that the folder is empty.

I would be more worried about this: When I search for an email address that I remember used to be in the now-empty folder,

Q: What is the name of the now-empty folder? Q: Is this an imap or pop mail account folder or a folder you created in 'Local Folders' account? Q: Have you repaired the index of that now-empty folder? Q: Did you recently compact that folder? If no, then do not compact it.

Q: Did you by any chance empty/delete etc emails from that now-empty folder or did it just suddenly appear emptied? Q: What Anti-Virus software are you using?

Hi Toad-Hall, Thanks for trying to help, but I'm afraid that I don't understand your questions about whether the folder is IMAP or POP or created in a local folder. I have not repaired or compacted the folder, at least not that I'm aware. I would not have deleted the emails from that folder; I just noticed they had disappeared. The folder is called "CCI Website", and it's actually a sub-folder. The other subfolders in the main folder all contain emails. I use Avast free anti-virus software. Many thanks again! Judi

General basic info on IMAP or POP:

Imap mail accounts see a remote view of the folders and their emails on the server. You subscribe to see those folders.

Pop mail accounts only access server Inbox and download emails into Thunderbird mail account Inbox.

Pop mail accounts can also be set up as deferred accounts more commonly called Global Inbox (Local Folders) where all emails are stored in the 'Local Folders' account and you do not see a separate pop mail account in the Folder Pane.

'Local Folders' is a special default mail account which contains the 'Outbox'. Outbox is used by all mail accounts if you ever choose the otion to 'Send Later'.

How to tell if you use IMAP or POP:

• Right click on the mail account name in the left Folder Pane and select 'Settings'
• select 'Server Settings' for that mail account
• At the top on the right, it will say : Server Type followed by either IMAP or POP mail server.

Please enable the following: 'Menu icon ' > 'Options' > 'Layout' > 'Select : 'Folder Pane Columns' or via Menu Bar 'Tools' > 'Layout' > 'Select : 'Folder Pane Columns'

Then select to show 'Size' column in Folder Pane. See image below as aid.

Post an image which shows the Folder Pane and 'Size' column details. Make sure the CCI Website folder and hierarchy is displayed.

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

still missing at least 2 local folders...no solution works.

I asked a question about missing messages a few months ago without receiving a reply.

Yesterday I noticed that it had happened again. This time I have identified a culprit. I suspect that my AV software, Forticlient, found a virus and quarantined the mailbox.

Perhaps you have something similar happening?