My Thunderbird version 140.8.0esr (32-bit) started to refuse sending mails this morning. The error message suggested to change the authentication method or if it still not working, my password could be stolen. I tried changing authentication method, it did not solved the problem so I changed it back to original setting as seen in the picture. I was afraid my account was hacked. I tried to send messages from my email account via other platform (the Web Mail service from the hosting company) and via my Android phone, mails sent successfully. So, my email account is safe. Since it is my business email account, I have been using it on Thunderbird daily for decades and I never encountered this problem before. Problem just started this morning. I tried to create a new Outgoing SMTP with same setting and deleted the old one, it didn't help. Although my Thunderbird refuse to send out mails, it receives incoming mails as usual. Hope someone can figure out this problem and help! Thanks in advance. Tim