User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0
Steps to reproduce:
Compose new email, click the send button.
Email address is ok, the send button is not greyed out, click send button, nothing seems to happen. Click File, Send later, nothing happens, nothing down the bottom of the window indicating that it's trying to communicate etc. I setup a password with Google, Thunderbird asks me to update password for IMAP, and it's saved in options, but at no stage will it ask for a new password for SMTP. It's like it's not trying to communicate with the SMTP server, but it doesn't complain that it can't communicate with the SMTP server either.
Ask for SMTP password, send messages.