Accent Issues in Sent Messages

Hello, For the past two days, the messages I send with Thunderbird are reaching their recipients without accentuated characters (they are replaced by ??). In the "Sent" folder, these messages appear correctly, and when I send from another account on the same computer, also using Thunderbird, they are correct as well. I went to the corresponding Yahoo site for the problematic account, and the messages sent from TB appear there with ??, but if I send a message directly from Yahoo, it reaches its recipient with accents. I deduce that it is the Yahoo account settings on TB that are causing the problem, but I can't find the error. I am working on Windows 10 and using Thunderbird 52.6.0 (32 bits). Can you help me?