Right-click the Inbox in the Folder Pane, Properties, select the Flags tab, as shown in the picture.

Thanks for this but it won't produce the dialogue box for the Properties folder when I right click on it.

I've tried troubleshooting mode. I've added FolderFlags and downloaded Thunderbird again but no luck so far.

Thanks again for the suggestion, mind.

I'm not familiar with right-click on macs, but you can also select Edit/Folder Properties. Press Alt if the Menu Bar with Edit is hidden. Check that FolderFlags is installed and enabled in the Add-ons Manager.

Thanks again SF but I can't access Folder Properties via the edit menu, on messages or via the Inbox drop-down menu. I think Alt on a PC is equivalent to CTRL click or right-click on a Mac, neither of which will give me access to the folder properties that can get me to FolderFlags, though via account settings and add- ons and themes, I can see that this is enabled.

https://support.apple.com/en-au/guide/mac-help/mh35853/mac

I can't do better than offer apples instructions.

A paste of the emails in question may be quite helpful. I have doubts that folder flags is the correct solution in this instance. I have recommended it in the past, but usually having a folder incorrectly identified as a drafts folder is in settings Account settings > Copies and folders for the account and over riding that with the addon just resets over and over as the two fight it out.

Thanks Matt,

The email provider's support service thinks there is a problem with my profile that is preventing access to these folders so I need a clean reinstall, rather than installing over the existing application and I might be better using Apple Mail, as this is taking up precious time.

The right clicks and control clicks in Apple don't seem to be a problem, it's something else within Thunderbird.

Thanks again,

Marcus