Hello

I don't quite see the problem in selecting 'other', then clicking the arrow at the end of your preferred account in the list to display the subfolders (and recursively the subfolders of a subfolder...)

GP, I agree with you that your explanation. But it needs to be done, asf ar as I understand, from the Thunderbir's account. And that for EACH email, to be put in a selected folder.

What I am looking for, is to select the folder for the sent email, when I click on "sent" upper left, when I finished writing my mail.

Or to explain it otherwise : when "clicklng" on "sent", Thunderbird would ask me where the mail needs to be archived : which folder or sub-folder. I choose then right folder/sub-folder or creating a new folder/sub-folder. That without reverting to Account > Copies & Folders to select destination.

I hope my explanation is more clearer

Obviously this is not a Thunderbird capability. Try to search for an add-on. This is not a need that I have ever seen asked for mail clients, so I'm not hopeful that such an add-on could be written and maintained.

See if this add-on helps:

https://addons.thunderbird.net/en-US/thunderbird/addon/copy-sent-to-current/