Here is how to set up your sent folder in Thunderbird
1. Thunderbird > Tools > Account Settings > Copies & Folders: set "Place a copy in" to "Sent Items" on the mail server
2. Restart Thunderbird.
Here is how to set up your sent folder in Thunderbird
1. Thunderbird > Tools > Account Settings > Copies & Folders: set "Place a copy in" to "Sent Items" on the mail server
2. Restart Thunderbird.