It looks like your email files(s) got 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 state of 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

Thanks for your response. Sorry, but this didn't solve my problem. Sent mails still do not appear in the send folder. White lines remain and all other white lines are time stamped with the last sent.

A slightly different approach: Close Thunderbird. Locate the index file in the file system (typically Sent.msf for the affected account), and delete it. It will be rebuilt when Thunderbird starts. Start Thunderbird.

Hello, First of all, thank you very much for your responses! In the meantime I had contact with my provider: it appears that they have a problem with the servers, which is why a number of customers have email problems. Apparently they've been working on it for days, but at the moment they haven't been able to fix it yet. So I'll just wait...

If they had a problem you might expect issues with other folders.

re: White lines remain and all other white lines are time stamped with the last sent.

Sounds like something is there, but not displaying. christ1 gave goof advise - Right-click the 'Sent' folder - Properties - Repair Folder

It is possible you have an invisible list.

If you select one of those lines with time stamped - where you expect subject etc to display, do you see email contents in the 'Message Pane' ?

Try this:

• Select folder so you see 'invisible list'.
• You will have various column headers visible eg: From, Subject ,Date.
• To the right of these column headers is the 'select columns to display' icon.
• click on the far right 'select columns to display' icon to see drop down options.
• Select 'Restore column order'

First of all, thanks for the suggestions and help! Since yesterday the error with the provider (!) has been fixed. All folders are complete again: the blank lines (since mid-December) have been completed again. But the 'new' mails that I sent during the problems are nowhere to be found and have not been sent. Case closed!...