That looks like a corrupt executable. Perhaps try reinstalling it. Where did you get your copy from? Perhaps you do not have all the dependencies installed.

The build distributed from Thunderbird.net has the following dependencies, but if the distribution is building it's own executable then the dependencies will be those of the distribution build.

   Thunderbird will not run at all without the following libraries or packages:
       GTK+ 3.14 or higher
       GLib 2.22 or higher
       Pango 1.22 or higher
       X.Org 1.0 or higher (1.7 or higher is recommended)
       libstdc++ 4.8.1 or higher
       glibc 2.17 or higher
   For optimal functionality, we recommend the following libraries or packages:
       NetworkManager 0.7 or higher
       DBus 1.0 or higher
       GNOME 2.16 or higher

I have updated MXLinux, unistalled and reinstalled Thunderbird and the problem remains. Thank you for your help. I will have to go back to Windows and pay 150 USD. I don't recommend linux.

I turned off Lightning for Thunderbird and the strange red messages disappeared. Anyway I switched to ClawsMail by now. Thank you for your help.