This is difficult to even describe. I have had a few instances where an email sent to say "John Doe", ends up having saved the body of an email that was sent to "Jane Doe" The Jane Doe email is always the email directly below the "John Doe" email. In some cases the preceding email was sent the day before or even older than that. In each instance the emails were definitely different, no copy and pasting was done, and the email looked as it should when it was finished being composed and the send button clicked. It seems that what ever processes Thunderbird does once send is pressed, something is going awry. This may have happened more than the few occasions that we have noticed, but in the cases that we have, it's because we have needed to refer back to the "John Doe" email and discovered that the body of the email is not what we wrote or sent. This is Thunderbird 60.6.1 on A Mac running High Sierra. Any help appreciated. Craig