You can see here a screenshot. I've opened the message and this is all I get. The tab reads the subject, but the contents are gone.

Thunderbird uses two files for mail. One to store the mail and another to populate the user interface. It is a sort of cache so a small file can be read instead of a large one.

What happens when the actual mail file becomes corrupt, or far more frequently is deleted for some reason by security software (anti virus) is what you describe. The display file still exists, but when your select the email nothing displays.

Right click the folder, select properties and then the repair button. That will force a refresh of the index/display file from the main mail store. The probable result is all your mails will cease to be listed. But that is the reality of what you have now. no mail and a spurious list.

You might want to look through the logs of your anti virus program and see if they deleted or quarantined a file called inbox.

Thank you Matt.

I was thinking that was the case. My antivirus did detect suspicious attachments and the log shows attempt to disinfect > failed > then deleted.

At least the number of messages lost is small, and I keep a backup.

Thanks