The 'lock' icon means you are using a secure method for connection. A padlock next to the account means Thunderbird has that account set up to use encryption (SSL/TLS) to connect to the remote server. It is a symbol that has been around for donkeys years and it is not a 'fake'. It has nothing to do with not being able to create folders. You should not be worried about it, indeed I would be more concerned if it was not there.

You do not say why you cannot create a folder. Could you provide a bit more info to help explain the issue.

Is the account a pop or imap mail account? When you create a folder, you can do this either as a top level folder under the mail account name or as a subfolders to another folder.

Are you trying to create a top level folder or a subfolder?

At which stage does it all go wrong? When you right click on the account name, do you see a drop down context menu with the option 'New Folder' ? Is 'New Folder' option greyed out ? If 'New Folder' is available, when you click on 'New folder' what happens, do you see a small window allowing you to enter name of folder? After entering the name and clicking on 'Create folder' button what happens? If you collapse the folder hierarchy by clicking on the small arrow to left of mail account name and then click again to show list of folders, does the suddenly folder appear? If imap account have you subscribed to see the folder?

Yesterday I transferred my email data from an old computer running Windows 7 to my new computer and laptop running Windows 10, according to your helpful video on how to do it correctly and replaced the files in the destination. I cannot now receive new messages and wondered what I did or didn't do yesterday

My iPad receives new emails though and when I sent an email from my Thunderbird account on my new computer it was sent to my iPad.

I saw by your previous replies that having a locked padlock on my email user name is not a problem. Any advice because I am stumped. Kind Regards Fiona