What happens when you search for the emails (presumably by using Edit - Find - Search Messages, or Ctrl-Shift-F) and you click the Open in Folder button below in the Seach dialog? That should take you to the message while jumping to the corresponding/lost folder on the left automatically.

Alternatively, you could use a file explorer to have a look in your Thunderbird Profile Folder and search for the message folder's name there. When viewing the Mail folder’s file tree/structure, it should become rather obvious where the newly created folder resides (at least for POP accounts.)

Or do you use IMAP, you created the folder on the ipad, and the created folder doesn't show up on the pc?

OK we're getting a little out of my comfort zone here, but I'll try to answer as best I can. Edit-Find-Search messages yields nothing. Search box at top of Thunderbird (Ctrl K) finds missing messages, and on the LHS under Filters/People/Folders/ it lists my missing folder and gives me the option to include or exclude it in the search. But I still cant find, or don't know how to find it in my list of email folders. I had a look at the profiles area, but couldn't find it there, although I'm not 100% sure I looked in the correct place. There does seem to be many less folders under my profile than actually exist, and are working, in Thunderbird. I might add that this problem is not new and has occurred in the past and I have ignored it. But I am now trying to get to the bottom of it.

It appears also, that I use IMAP, although I'm also pretty sure I created the folder on my PC, but may have added emails to it later from my ipad.

OK, apparently you referred to the Global Search option using CTrl-K, while I referred to the general/advanced way of finding messages that should use Ctrl-Shift-F for both Linux and Windows (see the Keyboard shortcuts - perform common Thunderbird tasks quickly article for shortcuts) and be accessible in the Edit menu on Windows and probably Linux as well. Note that where I wrote Edit - Find - Search messages above, that may be Edit - Search - Search Messages (my localized version uses the same verb for Find and Search). By using that option you'd get a search dialog displaying results in the lower pane including some buttons like the one mentioned above. Does that help?

For the profile data and folders: not every folder in Thunderbird is a real folder in the file explorer - they can be files as well as folders in the file system, at least for POP.

I haven’t got much experience on using both IMAP and POP for the same account on different devices, which may be related to the issue, so someone else may know more on that if this doesn’t help. IMAP should at least synchronize everything so that a created folder on one device should appear on the other, as opposed to POP, where one would manually need to create the same structure and things may go wrong when not. CoUld it be you use IMAP on the ipad only and POP on the pc?

Thanks for your reply Tonnes. I did try the Ctrl F search option, but there was nothing in the results. My Thunderbird Options Definitely says IMAP. Also doesn't seem to give an option to change it. I don't know if it should?

Imap accounts cannot be turned into POP mail accounts. You have to set them up as if separate mail accounts. But as you use other methods to access mail on server, it would be best to use IMAP.

First, can you double check that the Inbox subfolder you created is actually subscribed. right click on mail account name in Folder pane and select 'Subscribe'. you should see a list of all available folders. Make sure the new Inbox subfolder is subscribed. click on OK

Please confirm that the subfolder is subscribed. If you had to subscribe to see subfolder, then this should fix the issue.

If subfolder is already subscribed, do you synchronise all or only specified subscribed folders? 'Tools' > 'Account Settings' > 'Synchronization & storage' for imap mail account. OR right on mail account in folder pane and select 'Settings' then select: 'Synchronization & storage' for imap mail account.

See info at this link on the options of either allowing all folders to synchronise or specifying individual folders.

• https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage

If you have selected 'Keep messages for this account on this computer', then all folders will be synchronised. If this is not selected and you do not want all selected then you need to click on the 'Advanced' button to see list of folders to synchronise.

Make selection and click on all the 'OK's.

now that the subfolder is subcribed and synchronised, does it display in Folder Pane?

If all is subscribed and synchronised, but still not showing..... As you use IMAP this is where you would locate those profile folders and files. Do you see the files in your profile folder?

Make hidden files and folders visible:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

In Thunderbird

• Help > Troubleshooting Information
• click on 'show folder' button

A new window opens showing your profile folder name contents.

• Close Thunderbird now - this is important.

• click on 'ImapMail' folder
• click on mail account name folder

If you synchronise your subscribed fodlers then you would see mbox files that contain emails. Mbox files will have the same name as the folder. Mbox files have no extension. name of folder.msf files are just indexing files that do not have emails. name of folder.sbd folders are present when there are subfolders to a specific folder.

So an Inbox subfolder would be located in the 'Inbox.sbd' folder.

• click on 'Inbox.sbd' folder.

Can you see a file with no extension (mbox file with emails) that has same name as the missing subfolder? If yes, look for the *.msf file that has same name as subfolder and delete that .msf indexing file.

Now restart Thunderbird and report back on results.