Every time I have encountered this it has come down to either a flat battery on a mouse or keyboard or more commonly inadvertently pressing Ctrl+Enter which is the keyboard shortcut to send mail.

not that. did this maybe a year or so ago for quite some time. i think some programming change. very disruptive, if I am working on an email, get up to do something else, it gets sent when i am gone. must remember to remove the 'to' address in the beginning of email until ready to send.

Mozilla Thunderbird still sending emails when not completed when I walk away for a few minutes. More ideas? Thank you. Judith