If the account is IMAP, do the folders appear in the list if you right-click the account in the folder pane, Subscribe, click Refresh, and check the boxes for the folders (if they appear)?

I'm not clear on what it is - the folder under Profiles/Mail is called pop.clara.net which makes me think it's a pop account not IMAP but I'm not knowledgeable about these things.

It's probably a POP account; POP mail is stored in the Mail folder in the profile, with each account a subfolder such as pop.clara.net. You can also see the account type by selecting the account in the left pane of Tools/Account Settings, Server Settings, Server Type.

If you open the .sbd folder, do you see files with no extension (mbox files, which contain the mail content) and .msf index files with the same name?

Yes every file is there twice - no extension and .msf

Delete the .msf files with TB closed and restart TB, which will automatically re-index (recreate the msf files) the folders, and see if they appear as normal.

Sorry, my error. I chose a folder at random and it did have both file-types in. However all the folders that prompted my question and that are not visible in Thunderbird but which are visible in Windows Explorer only have the .msf files. Also, I've noticed that a lot of my other .sbd folders in Windows Explorer are empty yet I can see the emails in Thunderbird! Also I'm finding many sub-folders missing in Windows (not just the files in them but the whole folder) and yet they're visible in Thunderbird. However I it seems to be just these 5 sub-folders are missing in Thunderbird yet visible in Windows Explorer.

Your situation is quite odd. If you can't find an mbox file with the name of the 5 folders, and you didn't delete them to Trash in TB, I can't suggest where they might be. Is it possible you have a security program that scans mail folders and could have quarantined these folders? Do you have a backup of the profile folder that contains these folders?

I suppose my security programme might have done that although it would be odd it picked just those folders - I'll check. Unfortunately it's only since this problem occurred that I have learnt where the mail lives in Windows. So I've never backed it up before. it's a pity there isn't a simple command in Thunderbird to back up email (and ideally restore when needed) - that seems kind of essential :).

Just found some folders in the profile which have random'ish names (e.g. including ...01d348d3.sbd). They seem to contain my missing email files although dotted about a bit. If I copy the files without extension into the place they should be (where their equivalents already are with the .msf externsions) then I'll all the files in pairs (no extn version and .msf version) and in the right folders and sub-folders. I've done it with a few but of course they aren't visible as they're not indexed. I've done a 'Repair Folder' on the folder in question but they still don't appear. Any ideas?

Can you post images showing: All the Contents - files and folders - in 'pop.clara.net' folder and also all Contents of each *sbd folder

Copy one of the mbox files into Mail/Local Folders and then restart TB and see if they appear under Local Folders in the folder pane. You can also view an mbox file in a text editor to see if it still contains the message contents.

The best way to back up TB is to copy the Thunderbird folder to a safe location. On Windows, its default location is:

C:\Users\<winusername>\AppData\Roaming\Thunderbird

To restore the entire TB setup to the same or different computer, simply copy the Thunderbird folder into ...\Roaming.

There is an add-on that performs scheduled backups and can restore profiles from within TB:

https://addons.thunderbird.net/en-us/thunderbird/addon/importexporttools-ng/

I've backed up the profile, deleted the global index, re-installed Thunderbird which found the profile and gives me the same indexed emails I had before.

There are a few odd things going on here.

In Windows Explorer I see in the profile that I have an Inbox/Sam - General.sbd. And under that I have all the sub-folders and emails (both the message files and the appropriate matching.msf files). However in Thunderbird I don't see anything except the Sam - General folder itself and no sub-folders. Strangely it has 4 emails in it, which don't show up in WE.

There's also the strange thing in many ways the WE folder structure isn't anything like it is in TB. Some folders aren't there, some have weird names with lots of numbers inserted. However all the emails are fine in TB even though I can't find them in WE (except the 'Sam - General' file that started this thread).

Opening in Wordpad the files in General that I can see in WE do have the message contents in them.

Anyone got any ideas on this? Since the above I've also tried removing a .msf file from one email that isn't being 'seen' by TB. Then I deleted the global index and re-started TB. It re-created the global index but that .msf file didn't get re-created.

More info ... just found inbox.msf and deleted that as well as global-messages file, re-opened TB and saw it saying "building file for inbox" which seemed hopeful and then - nothing new. Un-seeable emails are still not seen by TB. This is driving me CRAZY. I have ALL my emails but TB won't see SOME of them even though it has a re-indexing system. Surely there's a solution?

Exit Thunderbird. access profile folders. In 'qkudlafn.default' folder. delete the following files.

• folderTree.json
• panacea.dat
• session.dat
• xulstore.json

Start Thunderbird.

Please report back on results.

No session.dat to delete (only session.json and sessioncheckpoints). Deleted other 3 and re-started. Those 3 were re-created but still no sign of the 'invisible' missing folders/files.

TRy: Select the 'Sam General' folder To the far right of column headers, there is a icon that facilitates choosing column headers. click on that icon and select: 'Reset column to default' option...note on recent version it may say 'Restore column order' .

Did it have any effect ?

Please post image showing contents of these folders:

• Mail\pop.clara.net\Inbox.sbd
• Mail\pop.clara.net\Inbox.sbd\Sam General.sbd
• Mail\pop.clara.net\Inbox.sbd\Sam General.sbd\GIGS.sbd

Restoring column order didn't have any effect. Images above show the Sam General and Gigs sub-folder structure. I've added one to show the inbox level too.

PS I really appreciate your time on this.