Thunderbird expects to have all emails in one place in the Profile folder. Can you please explain exactly how you are trying to restore/open the folders? Read Thunderbird Profile article for more information about how the Profile works, backing up restoring and moving the profile folder. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data Research about Local Folders in Thunderbird, as the Local Folder structure is meant for saving emails on your own local computer, separate from your live email accounts but accessible to Thunderbird. You may want to place those backed up emails in Local Folders - always assuming that the folders you are working with are actual email folders. If you could make a screen shot of the folders you are trying to restore then an expert may be able to advise further.

Thanks for the reply Agnes, That didn't do the trick I'm afraid. Another strange thing is that some of my emails are sorted in subfolders and in some of them each individual email is shown like it is a folder, which also makes no sense to me :/ Why is it important that my local email copies are in the specific Thunderbird directory when I can put in any directory in the program itself and tell it where to put local copies. Completely escapes me all.

There were two points there - it is important if you are restoring live email that it goes exactly where Thunderbird is directed to find the correct Profile. Then, as a separate point, Local Folders is a separate directory structure, and that is where you can put it where you want and direct Thunderbird to find it. In your original post you were rather vague, did not mention profile or local folders, just said you were "trying to restore and/or open them from there" - but you still have not explained exactly what you are doing, what backup method you used, where you are trying to put the lost emails or how you are doing that. If you don't provide specific information you are unlikely to get specific guidance to help your particular situation.