I may not be able to resolve this, but you need to post more info before anyone can assist. Please post the complete error message, plus screenshot of your SMTP server settings pane. Those will be helpful. Thank you

On this page, it states you need a separate 'app password' to use in TB in place of the account password.

"Note: When setting up in your email program, you will need an email program password."

Remove the entries for the account from Saved Passwords in Settings/Privacy & Security, restart TB, enter the 'app password' when asked for a password.

Otherwise, disable scanning of outgoing mail by your antivirus if it's on.