I can't send emails from my Talk 21 Account, but I can receive them.
I have my Talk 21 Account linked to Thunderbird. It has always worked well, but I can no longer send messages from this Account via Thunderbird although I can receive them.
If I want to send messages via Talk 21 then I either have to do this via the app on my phone or directly through Talk 21 (not using the email client).
I also have a Gmail Account linked to Thunderbird which works fine.