Check if indexing file has gone awry.

• Right click on 'Inbox and select 'Properties'
• click on 'Repair Folder'
• click on 'OK'

Check you do not have any filters selected. 'Quick Filter Bar' is usually the culprit, so make sure there are no selected icons in the Quick Filter Bar.

Check setting: 'View' > 'Messages' > 'All'

Check to see if the folder has invisible emails.

• select Inbox
• click near the top in the list area where you expect to see list of emails.

If email is displayed in the lower Message Pane then you have an invisible list.

• click on far right column header selection icon and select 'Reset Columns to default' from drop down options.

Clicking on Repair Folder had no effect There are no selected icons on the Quick Filter Bar ( but clicking on the 'Icon show only messages in your address book' displays emails). View Messages All is set and clicking near the top in the list area fails to show any invisible list. I have since updated Thunderbird and now the Inbox functions correctly.