If this is an IMAP account, are the missing folders not subscribed? Right-click the account in the Folder Pane, Subscribe..., Refresh, and see if the folders are available to be subscribed. Check also that View/Folders is All.

I appreciate the assistance, and I guess should have mentioned that it is a POP account.

When I right-click on the account in the folder pane at the left, I get this list of seven items: Get Messages, Open in New Tab, Open in New Window, Search Messages..., New Folder, Mark All Folders Read, and Settings.

I don't see "Subscribe" nor "Refresh," which perhaps are an IMAP-only features.

Also, I checked "Folders" in the "View" menu and discovered that "All" is and presumably always has been checked, given that I have not changed anything there ever.

What else can I do?

Yes, Subscribe is an IMAP-only feature. Help/Troubleshooting, Profile Folder, Open Folder, close TB, open the Mail subfolder and then the account subfolder, e.g. Mail/pop.gmail.com. Look for the mbox files, the large ones with no extension, named after folders, with like-named .msf index files. Look also in sbd subfolders and in Mail/Local Folders. Delete the .msf files, then restart TB, which will automatically rebuild the msf files, and see if the folders reappear.

In short, the folders did not return. Let me describe exactly what I did, hoping that it was what you directed.

I went to Help, selected Troubleshooting Information, found Profile Folder, clicked Open Folder (local drive), closed Thunderbird, opened the Mail subfolder, and then opened the account subfolder.

I'm not sure what "mbox" means, but I did see a string of relatively large no-extension files with accompanying .msf counterparts. I deleted the .msf files. I then looked at Local Folders under Mail and deleted .msf files there. Finally, I found one .sbd folder, Trash.sbd, which had an .msf file, which I deleted.

After restarting Thunderbird, I checked to see if any of the folders has been restored; they hadn't.

I did notice, however, that there was a duplicate account when I clicked Mail, different only by the inclusion of a "1" in the address and time-stamped exactly when I had clicked Open Folder (local drive) today. The original account was dated last year, probably the last time I had occasion to access the Profile Folder. I noticed that these two versions of the account appear to have entirely different, or at least substantially different folders. I figured I'd better give the same treatment to this version of the account, too, so I did, going through the same process as before and then restarting Thunderbird.

No files reappeared beyond the ones already there at the beginning of this procedure. I also noticed that none of the files I am missing were present in the account subfolder, the original account, if we may call it that, and the "1" account.

They must be hiding somewhere. What can be done next?

I think you did everything correctly. Check the Mail folder for other account subfolders, like Mail/pop.gmail-1.com, which is probably what you did. The subfolder that is active in the profile can be shown by selecting Server Settings for the account in Tools/Account Settings, then noting the Local Directory in the right pane.

It may be that the mbox files are corrupted and can't be read by TB. There are several 'mbox repair' tools, such as this one, that might be worth trying. Copy the repaired mbox into Mail/Local Folders, then restart TB.

I have this problem too on one of my 4 email accounts. These are IMAP accounts routed to TB from Outlook. All of a sudden a couple of days ago, except for Inbox and Trash, all the other folders had disappeared.

I went to Subscribe and checked all the folders I wanted back, then clicked on Subscribe, Refresh and OK, and nothing happened, When I went back to Subscribe, all the check marks on the folders were gone. I did this several times, varying just clicking on Subscribe or Refresh or both, nothing..

I then checked the Subscribe function in the other 3 accounts and all the folders I use had the check marks. Also, because the TB Sent folder is missing, while the actual send function works, the sent message cannot be placed in the Sent folder because it's not there.

Note that all the missing folders in TB are available and current in the Outlook account.

Any suggestion is greatly appreciated

I haven't quit or given up trying to resolve this--given what's missing, that would really be a bad idea--which the time between this and your last post might seem to have suggested. I tried the mbox repair tool you linked but found it difficult to figure out due to vague instructions (sometimes graced by interesting verbal formulations suggesting a less than full familiarity with English) that seemed to assume more knowledge on my part than I have.

So, I've looked around and have found another one that seems more user-friendly, at least for someone who is just beginning to understand something about these mbox folders/files. I'll try that next.

Is there any way to keep this disappearing file business from happening again?

But now, let me see if I can recover mbox files with this tool.

Regular profile backups are the best guard against data loss, as well as adding the profile folder as an exception or exclusion for any antivirus program.

I managed to restore nearly all of the vanished folders---thank you. I certainly will be more attentive to frequent profile backups.

To sfhowes:

Any suggestions for my disappeared folder issues?