More research results - sorry, I am discovering these aspects of Thunderbird only now...

Under C:\Users\Internet\AppData\Roaming\Thunderbird\Profiles\erumyxv8.Default User\Mail\pop.pt.lu, there is an Inbox file with Inbox.msf, both from today. I renamed Inbox.msf to have it re-created, but it did not help either.

re :Renaming global-messages-db.sqlite so that is re-created did not help. Both old and new global-messages-db.sqlite seem to contain the messages.

that file is just global search file and does not contain the actual emails. It is ok to delete that file as upon starting Thunderbird a new is created.

Inbox.msf is just an indexing file, it is required to be able to list and display all emails in Inbox (no extension) .

inbox (no extension) this is the file with emails.

I can send and receive mails, and read those newly received mails, but old mails are not accessible So you can see them listed in Inbox, but not select them ? At this point it is not known whether they are actually in the Inbox file.

There are two methods of forcing the eg: Inbox.msf file to relist the Inbox. 1. In Thunderbird right click on Inbox folder and select 'Properties' click on 'Repair folder' button click on OK Refresh the folder by selecting another and then reselecting.

2. NOTE: Thunderbird must always be closed / exited before doing anything in the Profile folder. In Profile Folder name > mail account name- delete the 'Inbox.msf' file. There is no point in keeping or renaming inbox.msf file, if it was not working in the first and it does not contain emails.

Restart Thunderbird and a new Inbox.msf file is created.

In Thunderbird Clear out cache. Tools > Clear Recent History

Now report back on what is displayed in the Inbox folder.

Make sure you have this view View > Folders > All

Toad-Hall, thanks for your answers. I had tried Repair before, and also tried to re-import the Inbox, but nothing worked.

This is what I finally did: The Inbox file obviously was damaged during the crash, and at one specific point contained a huge sequence (several MB) of NUL characters. Therefore Thunderbird could not read it properly anymore, I presume, and your proposals could not work, either. Removing these NUL characters left me with a working Inbox, but only from December 2014 on.

So I restored the previous versions of both Inbox and Inbox.msf (right-click the files in the Windows Explorer; most recent versions were from Tuesday due to a system update). With the mail list from the corrupt Inbox I could see that only one important mail was missing, and I managed to recover the content from the corrupt Inbox with Notepad++.

Finally I changed my server access options so that mails will be deleted from my provider's server only 2 weeks after download. Since I do weekly backups, this is more than enough time.