I’ve read all the archived queries about this issue. I’m running Windows 11, get my mail via POP, do use folders for sorting mail, but have an Inbox with way too many messages. Once this is fixed, I will do a better grooming the Inbox. The problem started three days ago as a result of my weekly backing up of Thunderbird using MozBackup. I found the very helpful reply by Toad-Hill on 11/7/23 to a similar query, and assume something got corrupted during the backup. (I’ve noticed that folder names get garbled sometimes after a backup.) Following Toad-Hill’s instructions, in Profile Folder > Mail > my-server, I’ve renamed “Inbox” as “OldInbox,” and a new Inbox shows as created in the folder for my mail server, along with a new Inbox.msf . Now when I open TB, OldInbox exists, and I can read the messages in it. It contained multiple copies of one new message, apparently downloaded every time I tried to Get Messages. BUT ... Inbox continues to show the same old list of emails that used to be there, doesn’t allow me to read any of them, and I still get the error message. Somehow TB isn’t using the new Inbox that was created in Profile Folder > Mail > my-server. I’ve tried clearing the startup cache to no effect. FWIW, I see that in Profile Folder > Mail > Local Folders, there’s an Inbox.msf dated over a year ago. The Sent.msf, Drafts.msf, and Trash.msf in Profile Folder > Mail > Local Folders are up to date. What do I do now? Is it safe and appropriate to copy the new Inbox.msf from Profile Folder > Mail > my-server into Profile Folder > Mail > Local Folders in place of the old Inbox.msf there?