Updated to 52.7. Still happening.

It sounds like your mail files are corrupted. First of all create a backup of your Thunderbird profile folder. https://support.mozilla.org/kb/profiles-tb#w_backing-up-a-profile

Then try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder

Note: depending on the corruption this may erase messages from the affected folder which cannot be recovered anymore. In that case you'd need to restore them from a recent backup done prior to the corruption.

Corruption is often caused by anti-virus software messing with Thunderbird mail files. It is therefore recommended to create an exception for the Thunderbird profile folder, so that the real-time scanner won't attempt to scan the profile with your mail.

For more information on the profile location see http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Also see http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

Thank you.

Emails that need to be kept are filed elsewhere. My (very) regular backup includes C:\Users\Ray\Appdata\Roaming\Thunderbird\

I have three email addresses and I repaired each inbox. [The problem was with at least two of these.] In each case there was a very brief flash of a window headed Thunderbird . . . (main email address (262MB) less than 1 second, others (<4kB) much less). I will report back if this solution has worked, or not.

Still getting the problem. Only noticed it in my primary address inbox so far.

If you have nothing in the inbox that you might want in the future, right click the inbox folder and select compact. You may loose nothing in the compact, or everything might be gone. That is the lottery of doing a compact on corrupted files.

Thank you Matt. Have backed up and compacted. Will wait and see what happens.

I'm still having the same problem. [So far I've repaired and compacted, at different times. Quite happy to try that again. Is there any preferred order to do this?]

If you can select individual messages in the troubled Inbox folder, you can try the 'real' fix. http://kb.mozillazine.org/Compacting_folders#Real_fix

"Real fix". The procedure sounds simple BUT:

When I looked for the inbox and inbox.msf files I found the following (fortunately listed on screen during the incremental backup procedure and with these paths I then found the originals): C:\Users\ray\AppData\Roaming\Thunderbird\Profiles\zmpezb8l.default\Mail\...(continued as below)

    pop3.ntlworld-1.com\Inbox
    pop3.ntlworld-2.com\Inbox
    pop3.ntlworld-4.com\Inbox
    pop3.ntlworld-6.com\Inbox
    pop3.ntlworld.com\Inbox
    pop3.virginmedia-1.com\Inbox
    pop3.virginmedia-2.com\Inbox
    pop3.virginmedia.com\Inbox

and the corresponding .msf files

By way of explanation my three email addresses are <name>@ntlworld.com (legacy) and are now hosted on virginmedia.com.

At first I thought the three email addresses were designated blank, -1 and -2. But where have the -4 and -6 files come from?

Which Inbox and Inbox.msf files should I delete? The problem is currently affecting only the primary email address.

After some thought I wondered if I should delete 'pop3.ntlworld.com\Inbox', 'pop3.virginmedia.com\Inbox' and the corresponding .msf files.

Your opinion please.

Which Inbox and Inbox.msf files should I delete? The problem is currently affecting only the primary email address.

Lookup the 'primary' account in account settings. At the top right of the Thunderbird window, click the menu button > Options > Account Settings - Server Settings

At the bottom is a field 'Local directory'. It will tell you which directory is in use for the account.

"Look up primary account." Sounds simple but there is no menu button, nor is 'Tools' > 'Options' any use.

Found the required page at 'Tools' > 'Account Settings' > 'Server Settings' > and then to 'Local Directory'. Gleaned that the @ntlworld.com addresses are given as User Name and 'pop3.virginmedia.com' is the Server Name in each case.

The local directories are pop3.virginmedia.com, pop3.virginmedia-1.com and pop3.virginmedia-2.com for primary, secondary and tertiary email addresses respectively.

Most recently the problem emails have appeared in only the primary address inbox so I deleted just C:\Users\Ray\AppData\Roaming\Thunderbird\Profiles\zmpezb8l.default\Mail\pop3.virginmedia.com\inbox and inbox.msf.

Re-started Thunderbird. Appears to be ok and received two emails in primary account, one of which was automaticaaly despated to my junk folder. [previous training].

Waiting to see if effective.

Sorry. My spelling has gone astray. For "automaticaaly despated" read "automatically dispatched".

Still getting these emails.

Just had another look on ISP's website. Earliest one there is 2016. [Really must do some deleting!]

I lost track of what your problem is and what you're trying to achieve.

Thunderbird displaying blank emails sent 01/01/1970. How do i stop them.

See: https://support.mozilla.org/en-US/questions/1212109?utm_campaign=questions-reply&utm_medium=email&utm_source=notification