Rated 5 out of 5 stars
I have been using this add-on for like ages as it makes the use of Thunderbird very convenient for me. I'm used to write e-mails, reviewing them (sometimes at a later time), and sending them all at once then. Without this add-on it's unnecassary complicated.
Thanks a lot for your advice! I didn't know that there was version 3.9.2 at all. The "All send" button is now back again!! Yay!