I recently upgraded to Mozilla Thunderbird 60.6.1. Since then when I open an email (in a new window), it automatically opens a second window in 'write mode'. This window contains the same message content, but also an error message at the bottom saying 'A unique identity matching the From address was not found. The message will be sent using the current From field and settings from identity <my email address>'. This is very annoying as each email I open now effectively opens two windows. I never experienced this issue in earlier versions of Thunderbird. How can I stop this from happening? Any suggestions anyone? Thanks in advance for your help.