Would you please post a screenshot? I'm having trouble visualizing what you're describing. Thank you.

hello David, as i told my Thunderbird shows left under: category the words sent (in German senden) and draft (in German Entwürfe) TWICE-times! as you can see now enclosed. Please advice/help who to eliminate this. kind regards B.Wolff

This usually happens when an email provider uses different names than the ones that Thunderbird assumes, such as Sent and SentFile. Make sure that in your account settings you define the ones you want. And then check to verify that thunderbird is just using those and not the other two. Once confirmed, you should be able to delete the others, either from within thunderbird or by closing thunderbird and deleting from within profile folder. There would be two entries for every folder, such as sent, and sent.msf. Sometimes it isn't easy. My email provider uses Drafts and Thunderbird assumes Draft, and it took some experimenting to figure which one could be deleted. I hope this helps.

One more thought: if IMAP, see if both are subscribed. if so, unsubscribe one. If just one is subscribed, delete the other.