Sent mails no longer saved in "Sent" folder
I've been happily using Thunderbird for a long time and now have version 115.12.2 (64-bit) on my MacBook Pro. It's old (10.14.6) but it's all I need. Until yesterday, TB worked fine. Suddenly, business emails stopped saving to my "Sent" Folder. I deleted a number of old emails and compacted the folder but that has not helped. I don't have the problem with other TB accounts. I checked the account settings:
Place a copy in "Sent" Folder on (my account) – as it always was.
I also checked "Show confirmation dialog when messages are saved". Despite seeing that, the message is NOT saved.
Are my sent mails from the last 24 hours saved anywhere? If so, how can I retrieve them?. How can I make sure they are saved in my "Sent" folder? Thanks so much!