I do not see my Sent messages using Thunderbird lately. Why?

A few days ago I sent emails and did not see the usual "Saving to Sent (IMAP)". Instead it said something like saving to Sent folder. That's fine, but the emails didn't appear in my Thunderbird Sent folders. I downloaded Thunderbird to see if my version was obsolete. Still no emails in Sent folder. The internet said I could delete my Sent folder, and Thunderbird would re-establish Sent folder. It did not. I can still see my old emails in my Local Thunderbird sent mail, so I deleted about 100 old emails in case the folder was too full. Still, the new emails I was sending did not appear. I checked with a few recipient people and they told me the email go to them. I have tried all the "solutions" I can find. What else can I do to see copies of my outgoing emails.?