Sent folder
I have been a Thunderbird user since way back in the Netscape days.
(1) I wrote about this a week or two ago.
My "SENT" messages STOP going into the "SENT" folder.
I can reset it by going to Tools / Account Settings / Copies & Folders and pushing the "Other" button & back to the "Sent" folder. Last time, the reset lasted a week or two. I don't know I have the problem until I try to find a sent message and it is not there.
(2) On my Wife's Thunderbird, when she has pushed the "Spam" button for a message in the "Inbox" - The message does go to the "Spam" folder.
How does she mark them as "Not Junk" ?
She marks ALL of the messages she wants back in the "Inbox" - BUT - The messages she has tried to make "Not Junk" continue going to the "Spam" folder the next time received.