Hello there We have read the message. We try to help you. https://support.mozilla.org/en-US/kb/cannot-send-messages#:~:text=Verify%20that%20your%20outgoing%20email%20is%20not%20being%20blocked%20by,and%20sending%20another%20test%20email. if these answers have been read by you and nothing has changed in them. check if the security tools you are using are included. If they can be disabled for once and start Thunderbird without them this time see if this has offered a solution. will you reply back to me afterwards? Greetings Firefox volunteer